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PRINCIPLES 

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IRRIGATION  ENGINEERING 


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PRINCIPLES 

OF 

IRRIGATION    ENGINEERING 


ARID  LANDS,  WATER  SUPPLY,  STORAGE 

WORKS,  DAMS,  CANALS,  WATER 

RIGHTS  AND  PRODUCTS 


BY 

FREDERICK  HAYNES  NEWELL 

DIRECTOR   U.    8.    RECLAMATION   SERVICE. 

AND 

DANIEL  WILLIAM  MURPHY 

A.  B.,  A.  M.,   PH.  D. 

ENGINEER  IN  CHARGE  OF  DRAINAGE  U.  8. 
RECLAMATION  SERVICE. 


FIRST  EDITION 
FOURTH  IMPRESSION 


McGRAW-HILL  BOOK  COMPANY,  INC. 

NEW  YORK:    239   WEST  39TH  STREET 

LONDON:    6  &  8  BOUVERIE  ST.,  E.  C.  4 

1913 


LIBRARY 

UNIVERSITY  OF  CALIFORNIA 


COPYRIGHT,  1913,  BY  THE 
MCGRAW-HILL  BOOK  COMPANY 


THE. MAPLE. PRESS. YORK. PA 


PREFACE 

In  the  following  pages  an  attempt  is  made  to  give  an  outline  of  the 
fundamental  questions  involved  in  undertaking  and  carrying  out  an 
irrigation  enterprise.  In  presenting  this  matter  in  the  form  of  a 
treatise  on  Irrigation  Engineering,  it  is  intended  primarily  for  the  use 
of  students  and  engineers  who  desire  to  become  acquainted  with  the 
general  principles  involved  in  considering  the  feasibility  of,  and 
in  planning,  constructing  and  operating  irrigation  systems.  An 
attempt  has  also  been  made,  however,  to  present  the  subject  mat- 
ter in  such  form  that  it  may  be  read  with  profit  by  persons  inter- 
ested in  irrigation,  but  without  a  thorough  technical  knowledge  of 
the  subject  of  hydraulics. 

It  is  not  possible  in  a  "book  of  ordinary  length,  to  go  into  all  of  the 
details  essential  to  successful  irrigation  construction  and  operation. 
The  broader  and  more  general  aspects  of  the  subject  therefore  are 
presented  with  the  assumption,  that  where  further  details  are  neces- 
sary, it  will  be  possible  for  the  student  to  find  them  in  one  of  the  many 
technical  books  now  available.  The  purpose  of  the  work  is  therefore 
to  assist  the  student  and  engineer  by  pointing  out  the  essential  ques- 
tions to  which  special  attention  must  be  given. 

In  attempting  to  give  this  broad  survey,  the  presentation  has  been 
made  as  simple  and  concise  as  possible.  It  is  appreciated  that  even 
with  engineers  of  large  experience,  there  are  certain  broad  principles, 
which  though  elementary,  are  worthy  of  frequent  reconsideration. 
These  principles  when  applied  to  new  problems  are  frequently  sug- 
gestive of  different  viewpoints  and  lead  to  a  more  thorough  under- 
standing of  the  work  in  hand.  The  designation,  "The  Principles  of 
Irrigation  Engineering,"  has  thus  been  selected  as  indicative  of  the 
attempted  scope  of  the  work. 

Irrigation  Engineering  in  its  broadest  aspects  may  be  defined  as 
the  development  of  the  water  resources  of  the  arid  regions  as  relating 
to  their  conservation  and  use  as  a  part  of  the  wealth  of  the  nation. 
More  specifically,  it  deals  with  the  methods  of  holding,  controlling 
and  distributing  the  waters  needed  in  agriculture,  and  further,  those 
matters  which  lead  to  financial  success  in  the  investments  then 
made.  As  a  science  or  branch  of  knowledge,  it  is  the  result  of 

v 


vi  PREFACE 

investigations  worked  out  and  information  collected  and  systema- 
tized. It  should  furnish  knowledge  concerning  the  water  supply 
and  its  use,  especially  as  applied  to  human  needs  and  happiness. 
It  may  be  studied  from  the  point  of  view  of  the  statesman  con- 
cerned with  questions  of  public  welfare,  by  the  capitalist  seeking 
an  investment,  and  by  the  engineer,  called  upon  to  plan  irrigation 
works. 


CONTENTS 

PAGE 
PREFACE    v 

LIST  OF  PLATES xi 

CHAPTER  I 

IRRIGATION i 

Definition — History  and  development — Needs  and  benefits — Methods 
of  irrigation — Comparison  of  irrigated  and  non-irrigated  lands. 

CHAPTER  II 

IRRIGABLE  LANDS 8 

Arid  region — Topographic  features — The  soil — Preparation  of  lands — 
Location — Intensive  farming — Climate. 

CHAPTER  III 

WATER  SUPPLY 15 

Source  of  water  supply — Character  of  supply — Benefits  of  control — 
Study  of  water  supply — Rainfall — Runoff — Influences  affecting  runoff 
— Character  of  watershed — Evaporation — Runoff  on  different  water- 
sheds— Comparison  of  runoff — Measurement  of  water — Units  of 
measurement — Convenient  equivalents — Methods  of  measurement — 
Results  of  stream  measurement — Quality  of  water  supply — Amount  of 
water  required  for  irrigation 

CHAPTER  IV 

DESIGN  AND  CONSTRUCTION  OF  CANALS 

Capacity — Location  of  canals — Alignment — Cross-section — Slopes  and 
width  of  banks — Material  for  banks — Grades  and  velocities — Excava- 
tion— Specifications  for  excavation — Protection  against  seepage  in 
canals — Lined  canals — Roadways  on  banks — Lateral  drainage — Right- 
of-way  for  canals. 

CHAPTER  V 

CANAL  STRUCTURES 61 

Classification — Permanent  and  temporary  structures — Headgates — 
Operating  device — Turnouts — Checks  and  drops — Wasteways — Cul- 
verts— Flumes — Velocity  and  flow  of  water  in  flumes — Tunnels — Lining 
— Inverted  siphons — Bridges — Measuring  devices — Screens — Protec- 
tion of  canal  structures. 

vii 


viii  CONTENTS 

CHAPTER  VI 

PAGE 

DISTRIBUTION  SYSTEMS 102 

Canals  and  laterals— rGeneral  plan  of  distribution  system — Topo- 
graphic surveys  for  lateral  systems — Capacity  of  laterals — Location  of 
laterals — Cross-secton  of  laterals — Points  of  delivery  of  water — Delivery 
box — Flumes  and  pipe  distributaries — Accessibility  to  laterals. 

CHAPTER  VII 

IRRIGATION  BY  PUMPING 116 

General  conditions — Source  of  supply — Character  of  pumps — Power 
for  pumping — Wind-mills — Steam  power — Gasoline  and  oil — Water 
power — Compressed  air — Hydroelectric  power — Cost  of  pumping — 
Feasibility  of  pumping. 

CHAPTER  VIII 

DRAINAGE 136 

Classification — Needs  of  drainage — Alkali  and  its  effect — Benefit  of 
drainage — Ground  water — Effects  of  drainage  on  soils — Open  and  closed 
drains — Relief  and  intercepting  drains — Drainage  investigations — 
Capacity  of  drains — Depth  of  drains — Distance  between  drains — 
Grades  and  velocities  of  flow  in  drains. 

CHAPTER  IX 

OPERATION  AND  MAINTENANCE 152 

Distribution  of  water — Continuous  flow — Periodic  rotation — Length 
of  irrigation  season — Frequency  of  irrigation — Duty  of  water — Measure- 
ment of  water  used — Human  element — Maintenance — Priming — Care 
of  banks — Cleaning  canals — Organization  for  operation  and  mainte- 
nance— Records — Costs. 

CHAPTER  X 

STORAGE  WORKS 170 

Determination  of  storage  supply — Annual  runoff — Amount  of  runoff 
that  can  be  stored — Seepage  losses — Evaporation  losses — Ratio  of 
runoff  to  the  storage  capacity — Determination  of  storage  required — 
Economic  questions  in  storage-^-Cost  of  storage 

CHAPTER  XI 

RESERVOIR  JITES 185 

""""General  requirements — Survey  of  Reservoir  sites — Contour  maps — 
Computation  of  capacities — Choice  of  reservoir  site — Shallow  and 
deep  reservoirs. 


CONTENTS  ix 

CHAPTER  XII 

PAGE 

DAM  SITES 190 

General  conditions — Surveys  of  dam  sites — Foundation — Borings  and 
test  pits — Character  of  foundations — Character  of  materials  for  con- 
struction— Accessibility  of  materials  for  construction — Spillway — 
Records  of  stream  flow — Kind  of  dam  best  adapted  to  suit  conditions. 

CHAPTER  XIII 

TIMBER  DAMS 200 

Kinds  of  dams — Early  stages  of  development — Use  of  timber  dams — 
Where  timber  dams  are  applicable — Conditions  of  Stability — Water- 
tightness — Types  of  timber  dams — Log  and  brush  dams — Crib  dams — 
Crib  and  pile  dams — Framed  dams — Limits  of  height. 

CHAPTER  XIV 

EARTH  DAMS 211 

Site  for  earth  dams — Foundation — Selection  of  materials — Section  of 
dam — Prevention  of  seepage  under  dam — Placing  of  materials  in  the 
dam — Placing  of  materials  by  hydraulic  method — Compacting  the  mate- 
rial— Prevention  of  seepage  through  the  dam — Core  wall — Puddle 
core — Water-tight  face — Cut-off  trenches — Protection  of  slopes — 
Drainage  of  dam — Dikes — Limits  of  height  of  earth  dams — Ex- 
amples of  earth  dams. 

CHAPTER  XV 

ROCK-FILL  DAMS 220 

Description — Advantages  over  earth  dams — Site  to  which  adapted — 
Foundation — Materials — Section  and  slopes — Water-tight  section. 

CHAPTER  XVI 

MASONRY  DAMS 232 

Principles  of  Construction — Kinds  of  masonry  dams — Rubble  concrete 
— Foundations — Section — Concrete — Upward  pressure — Curved  dams 
— Multiple  arch  dams — Internal  stresses — Safe  limits  for  foundations — 
Overflow  dams — Protection  of  lower  toe  from  erosion — Safe  heights — 
Typical  masonry  dams. 

CHAPTER  XVII 

OUTLET  WORKS 248 

Capacity — Location — Location  of  gates — Gate  towers — Operation  of 
gates — Erosion  due  to  high  velocities — Vibration  of  gates— Character  of 
gates — Fishways — Spilling  requirements — Spillway  design — Determi- 
nation of  capacity — Location  and  type — Grades  and  velocities — Pro- 
tection against  erosion. 


x  CONTENTS 

CHAPTER  XVIII 

PAGE 

WATER  RIGHTS 263 

Definition — Origin  of  water  rights  in  the  United  States — Riparian 
rights — Acquisition  of  water  rights — Theory  upon  which  granted — 
Beneficial  use  of  water — Water  rights  apart  from  lands. 

CHAPTER  XIX 

ECONOMIC  FEATURES  OF  IRRIGATION 275 

Feasibility  of  irrigation — Fundamental  questions  to  be  considered — 
Value  of  land — Increase  in  value — Soil,  climate  and  crops — Permanence 
of  water  supply — Cost  of  constructing  works — Other  costs — Markets 
and  transportation  facilities — Security  of  investment — Ultimate  results. 

INDEX  .   286 


LIST  OF  PLATES 

FACING  PAGE 
PLATE  I 4-5 

Fig.  A. — Diverting  dam  in  the  Boise. River,  Idaho,  a  typical  structure  for 
taking  out  river  water  by  gravity. 

Fig.  B. — Main  northside  canal  of  Minidoka  Project,  Idaho,  illustrative  of 
the  larger  irrigation  canals,  with  power  transmission  lines  located  on  the 
bank. 

Fig.  C. — Water  being  distributed  to  the  fields  through  furrows  after 
having  been  diverted  from  the  river  by  gravity  canals. 

Fig.  D. — Water  being  applied  to  the  fields  by  flooding. 
PLATE  II 26-27 

Fig.  A. — A  method  of  making  a  measurement  of  the  amount  of  water  in  a 
stream,  using  current  meter  from  bridge. 

Fig.  B. — Making  similar  measurements  by  wading. 

Fig.  C. — Meters  used  for  measuring  the  velocity  of  the  flowing  water. 
PLATE  III 48-49 

Fig.  A. — Constructing  canal  in  earth  by  means  of  four-horse  Fresno 
scrapers,  Minidoka  Project,  Idaho. 

Fig.  B. — Throwing  up  small  laterals  by  means  of  four-horse  road  ma- 
chine, Huntley  Project,  Mont. 

Fig.  C. — Excavating  canal  by  use  of  excavator  with  belt  conveyor,  drawn 
by  traction  engine,  Belle  Fourche  Project,  S.  Dak. 

Fig.  D. — Finished  canal  with  both  upper  and  lower  banks,  Lower  Yellow- 
stone Project,  Mont. 
PLATE  IV 54-55 

Fig.  A. — Enlarging  canal  by  means  of  floating  dipper  dredge,  Salt  River 
Project,  Ariz. 

Fig.  B. — Enlarging  canal  by  use  of  excavator  with  drag-line  working  from 
one  side  of  canal,  Salt  River  Project,  Ariz. 

Fig.  C. — Lining  canal  with  concrete  to  increase  the  capacity  and  reduce 
the  seepage,  Boise  Project,  Idaho. 

Fig.  D. — Concrete   lined   canal   in   shattered   rock,    carrying    water   of 

Truckee  River  to  Carson  River,  Truckee-Carson  Project,  Nevada. 
PLATE  V 62-63 

Fig.  A. — Wooden  headgates,  typical  of  those  usually  built  for  the  earlier 
canals,  Jordan  and  Salt  Lake  City  canal,  Utah. 

Fig.  B. — Concrete  headworks  with  steel  gates,  Interstate  canal,  North 
Platte  Project,  Neb. 

Fig.  C. — Concrete  headworks  and  roadway,  Mesilla  Valley  canal,  Rio 
Grande  Project,  New  Mexico. 

Fig.  D. — Concrete  headworks  with  sluice  gates  at  Lagiina  dam  on  Colo- 
rado River,  Ariz.-Cal. 

xi 


xii  LIST  OF  PLATES 

FACING  PAGE 

PLATE  VI 80-8 1 

Fig.  A. — Series  of  checks  and  drops  with  inclined  chutes  terminating  in 

water  cushion  with  concrete  blocks  to  break  the  force  of  the  water, 

North  Platte  Project,  Neb. 
Fig.  B. — Notched  check  and  drop  with  projecting  lip  beneath  each  notch 

to  diffuse  and  break  the  force  of  the  falling  water,  Rio  Grande  Project, 

New  Mexico. 
Fig.  C. — Concrete  chute,  built  instead  of  a  series  of  drops,  and  terminating 

in  a  water  cushion  with  concrete  baffle  board,  Boise  Project,  Idaho. 
Fig.  D. — Spillway  lip  to  automatically  permit  escape  of  excess  water  from 

canal  back  into  river  and  sluice  gates  provided  to  facilitate  scouring  out 

of  materials  deposited  in  upper  portion  of  canal,  Salt  River  Project, 

Ariz. 

PLATE  VII       88-89 

Fig.  A. — Concrete  flume  carrying  water  of  main  canal  across  side  drainage 

lines,  North  Platte  Project,  Wyo.-Neb. 
Fig.  B. — Concrete  inverted  siphon  carrying  water  of  main  canal  under  side 

drainage  line  instead  of  over  it,  North  Platte  Project,  Wyo.-Neb. 
Fig.  C. — Concrete  pressure  pipe  used  in  place  of  flume,  Sun  River  Project, 

Mont. 
Fig.  D. — Metal  flume  on  timber  trestle. 

PLATE  VIII     iio-in 

Fig.  A. — Distributing  laterals  with  wooden  boxes  and  gates,  typical  of 

the  pioneer  work  in  irrigation,  Yakima  Project,  Wash. 
Fig.  B. — Concrete  box  and  drop  on  distributory  in  place  of  earlier  form  of 

wooden  construction,  Orland  Project,  Cal. 
Fig.  C. — Cast-iron  valves  on  distributing  system  instead  of  the   usual 

wooden  gates,  Uncompahgre  Project,  Colo. 

Fig.  D. — Farmer  water  gates  on  concrete  inclined  slabs,  Sun  River  Proj- 
ect, Mont. 

PLATE  IX 124-125 

Fig.  A. — Pumping  water  by  wind  mill  into  earth  tank  from  which  an 

irrigating  stream  can  be  had. 
Fig.  B. — Gasoline  pumping  equipment. 
Fig.  C. — Generators  driven  by  water  power,  furnishing  electrical  energy 

for  pumps,  Minidoka  Project,  Idaho. 
Fig.  D. — Electrically  operated  centrifugal   pumps   delivering   water  to 

laterals  on  Gila  River  Indian  Reservation,  Ariz. 

PLATE  X  ....". 138-139 

Fig.  A. — Alkali  flat,  formerly  a  valuable  farm,  now  ruined  by  careless 

irrigation  and  lack  of  drainage. 
Fig.  B.— Distributory  lined  with  concrete  to  reduce  loss  of  water  and 

prevent  development  of  alkali. 

Fig.  C.— Weir  and  self-registering  gage,  Williston  Project,  N.  Dak. 
Fig.  D.— Automatic  gage  for  recording  height  of  water  in  river  or  main 

canal,  Laramie  River,  Colo. 

PLATE  XI 192-193 

Fig.  A.— Storage  dam  site,  Roosevelt  Dam,  Salt  River  Project,  Ariz. 


LIST  OF  PLATES  xiii 

FACING  PAGE 

Fig.  B. — Drilling  for  bed  rock  at  storage  dam  site,  Shoshone  Project,  Wyo. 
Fig.  C. — Spillway  of  Bumping  Lake  dam,  Yakima  Project,  Wash. 
Fig.  D. — Spillways  of  Roosevelt  Dam,  Salt  River  Project,  Ariz. 

PLATE  XII 202-203 

Fig.  A. — Brush  and  stone  dam,  typical  of  pioneer  conditions,  Las  Cruces 

canal,  Rio  Grande  Project,  New  Mexico. 
Fig.  B. — Log  and  earth  dam,  Cimarron  River,  New  Mexico. 
Fig.  C. — Foundations  for  timber  dam,  Yakima  Project,  Wash. 
Fig.  D. — Apron  of  partly  finished  timber  dam,  Yakima  Project,  Wash. 

PLATE  XIII 214-215 

Fig.  A. — Foundations  for  earth  dam,  showing  excavations  for  puddled  core 

and  earth  being  brought  to  the  site  by  railroad  train,  then  distributed 

and  rolled  in  thin  layers,  Umatilla  Project,  Oregon. 
Fig.  B. — Earth  dam  partly  protected  by  heavy  gravel  on  water  side, 

Boise  Project,  Idaho. 

Fig.  C. — Hydraulic  construction  of  earth  dam;  giant  in  foreground  wash- 
ing earth  and  small  rocks  into  flume  supported  on  trestles  and  conveying 

materials  to  site  of  dam,  Okanogan  Project,  Wash. 
Fig.  D. — Completed  dam  built  by  hydraulic  process. 

PLATE  XIV 224-225 

Fig.  A. — Concrete  core  wall  in  earth  dam,  Carlsbad  Project,  New  Mexico. 
Fig.  B. — Loose  rock  protection  of  earth  dam  on  water  side,  Umatilla 

Project,  Oregon. 
Fig.  C. — Paving  on  water  side  of  earth   embankment,   Belle  Fourche 

River,  S.  Dak. 
Fig.  D. — Concrete  block  protection  against  wave  action  on  earth  dam, 

Belle  Fourche  Project,  South  Dak. 

PLATE  XV 234-235 

Fig.  A. — Earth  and  rockfill  dam  under  construction,  with  low  concrete 

core  wall,  gravel  and  earth  is  being  dumped  on  upper  side  with  loose 

rock  below,  Minidoka,  Idaho. 
Fig.  B. — Concrete  structure  for  regulating  floods,  East  Park  dam,  Orland 

Project,  Cal. 

Fig.  C. — Rubble  masonry  dam,  lower  portion  of  Roosevelt  Dam,  Arizona. 
Fig.  D. — Foundations  for  Lahontan  Dam,  Nev.     View  showing  concrete 

conduit,  conveying  water  through  lower  part  of  dam,  with  conveying 

plant  in  background. 

PLATE  XVI 252-253 

Fig.  A. — Gate  tower  and  bridge  from  earth  dam,  forming  Cold  Springs 

Reservoir,  Umatilla  Project,  Oregon. 
Fig.  B. — Grillage  protecting  entrance  to  gates.     Pathfinder  Reservoir, 

North  Platte  Project,  Wyo. 
Fig.  C. — Spillway  with  effective  lengths  increased  by  curved  outlines, 

Oreland  Project,  Colo. 
Fig.  D. — Spillway  for  earth  dam,  Belle  Fourche  Project,  S.  Dak. 


PRINCIPLES  OF  IRRIGATION  ENGINEERING. 

CHAPTER  I 
IRRIGATION 

Definition. — Under  the  term  " irrigation,"  as  applied  to  agricul- 
ture, is  included  all  of  the  operations  or  practices  in  artificially 
applying  water  to  the  soil  for  the  production  of  crops. 

Irrigation  at  the  present  time,  considered  from  the  standpoint  of 
the  irrigation  engineer,  includes  the  conservation  and  storage  of  the 
water  supply,  the  carrying  of  water  from  the  source  of  supply  to  the 
irrigable  area  and  distributing  it  to  the  lands.  It  involves,  in  many 
cases,  the  development  and  bringing  to  the  surface,  waters  from 
underground  sources,  and  also  the  raising  of  water  by  pumping  or 
other  means  to  lands  which  cannot  be  reached  by  a  gravity  flow 
from  the  source  of  supply.  Closely  related  to  irrigation  is  also  the 
question  of  drainage  for  the  removal  of  excess  waters  from  the  land. 

Drainage,  either  by  natural  or  artificial  means,  is  equally  as 
important  as  irrigation  to  insure  successful  agricultural  operations. 
It  is  generally  impracticable  to  apply  water  to  lands  sufficient  to 
grow  crops  without  a  portion  of  it  being-  wasted  either  on  the  surface 
or  underground.  This  waste,  or  excess,  must  be  removed  either 
through  natural  outlets  or  artificially  constructed  drainage  ditches, 
in  order  to  prevent  the  land  becoming  waterlogged  or  charged  with 
alkali  and  rendered  unfit  for  successful  farming. 

In  addition  to  the  physical  problems  involved  in  irrigation, 
economic  questions  must  also  be  considered.  These  questions  in- 
volve estimates  on  the  value  of  lands  to  be  irrigated  and  a  comparison 
of  these  values  with  the  cost  of  constructing  irrigation  works  in 
order  to  determine  whether  the  project  is  feasible  from  a  financial 
standpoint. 

History  and  Development. — The  practice  of  irrigation  is  older  than 
civilization.  It  originated  doubtless  in  the  semi-tropical  and  rela- 
tively arid  regions,  where  there  is  a  periodic  overflow  of  the  desert 
areas  traversed  by  some  of  the  large  rivers  like  the  Nile.  These 
streams,  coming  from  plateau  or  mountain  regions,  are  swollen  by 
seasonal  rains  or  melting  of  snow.  Mankind  in  the  early  stages  of 

1 


2         PRINCIPLES  OF  IRRIGATION  ENGINEERING 

development  learned  to  guide  or  assist  this  overflow  by  rough  dikes 
and  rudely  constructed  ditches,  later  building  canals  to  bring  the 
water  out  to  lands  which  would  not  be  overflowed  naturally,  and 
thus  gradually  becoming  independent  of  the  natural  rise  of  the 
stream.  Before  historic  times  the  practice  of  irrigation  had  been 
recognized  to  such  an  extent  that  rules  relating  to  the  handling  of 
water  were  embodied  in  the  earliest  of  known  writings.  In  the  code 
of  Hammurabi  (2250  B.  C.)  it  appears  that  provisions  were  made  to 
cover  similar  troubles  and  controversies  that  are  being  met  to-day. 
Laws  concerning  the  distribution  of  water  and  guarding  against  waste 


FIG.  I. — Humid  regions  of  the  world,  indicated  in  black;  arid  or  non-productive 
regions  indicated  by  uncolored  land  areas. 

or  damage  to  a  neighbor's  field  through  carelessness  may  be  copied 
and  applied  to  modern  conditions  from  the  oldest  of  recorded  regu- 
lations. In  nearly  all  of  the  countries  bordering  the  Mediterranean 
and  to  the  east  in  Mesopotamia,  India  and  China,  the  art  of  irri- 
gation was  practised.  The  early  writings  on  the  discovery  and  con- 
quest of  Mexico  and  of  South  American  countries  casually  mention 
the  irrigation  canals  as  part  of  the  features  of  the  country. 

The  relative  location  and  extent  of  the  humid  regions  of  the  world 
are  indicated  by  the  black  areas  on  the  accompanying  diagrammatic 
map  (Fig.  i).  This  illustrates  how  small  are  these  humid  areas, 
as  compared  with  the  total  land  surface  enclosed  within  the  outlines 
and  left  blank  as  indicating  conditions  where  plant  life  is  dependent 


IRRIGATION  3 

largely  upon  an  artificial  supply  of  water  or  where  the  climate  is 
too  cold  for  the  production  of  most  of  the  ordinary  crops.  As  in- 
dicated on  this  diagram,  the  greater  part  of  western  Asia  and  the 
Mediterranean  countries  within  which  civilization  has  developed 
are  arid  or  semi-arid;  also  the  greater  part  of  the  western  half  of  North 
America  including  a  considerable  portion  of  Canada,  Mexico,  and 
the  United  States. 

In  the  southwestern  portion  of  the  United  States,  especially  in 
Arizona  and  New  Mexico,  remains  of  irrigation  works  have  been 
found  which  were  constructed  and  operated  prior  to  any  recorded 
history  of  that  section.  In  the  valley  of  the  Rio  Grande,  irrigation 
was  practised  by  the  native  inhabitants  before  the  advent  of  Spanish 
explorers  in  the  early  part  of  the  sixteenth  century.  The  early 
Spanish  missionaries  also  constructed  irrigation  works  in  that  valley 
some  time  during  that  century.  This,  so  far  as  known,  was  the  begin- 
ning of  modern  irrigation  in  the  United  States.  Some  of  the  works 
constructed  by  the  early  Spanish  settlers  have  been  in  use  almost 
continuously  up  to  the  present  time. 

In  1847,  irrigation  was  begun  by  the  Mormon  settlers  in  the  Salt 
Lake  Valley,  Utah.  This  was  the  beginning  of  Anglo-Saxon  irriga- 
tion in  this  country.  The  next  irrigation  development  of  any  mag- 
nitude was  about  twenty  years  after  work  was  started  in  Utah, 
when  it  was  taken  up  in  Colorado  and  California.  From  these 
parent  colonies  it  gradually  spread  to  the  other  states  of  the  arid 
west. 

The  first  attempts  at  irrigation,  as  previously  stated,  were  primi- 
tive in  character  and  consisted  principally  in  assisting  nature  in 
carrying  water  over  the  low  bottom  lands  during  the  flood  period. 
The  next  step  was  the  diversion  of  water  from  the  streams  and  con- 
ducting it  by  means  of  crudely  constructed  canals  to  the  lands.  The 
first  ditches  constructed  throughout  the  west  consisted  of  simple 
furrows  for  turning  part  of  the  flow  of  a  creek  to  the  low-lying  bottom 
lands.  Diversion  works,  in  many  cases,  consisted  of  temporary 
dams  of  bags  of  sand  placed  in  the  stream  to  raise  the  water  slightly 
and  divert  it  to  the  canals.  When  not  in  use,  canals  were  frequently 
closed  by  means  of  an  earthen  embankment.  When  water  was 
desired  in  the  canal,  the  embankment  was  wholly  or  in  part  removed. 
In  the  construction  of  these  early  canals  engineering  advice  was 
rarely  sought,  grades  were  fixed  by  the  eye  or  by  the  flow  of  water 
and  locations  made  to  conform  to  the  contours  of  the  slopes. 

In  general  it  may  be  said  that  the  advances  in  irrigation,  the  oldest 


4          PRINCIPLES  OF  IRRIGATION  ENGINEERING 

of  agricultural  practices,  have  been  made  but  slowly.  It  was  not 
until  comparatively  recent  times  that  the  larger  problems  pertaining 
to  storage  and  conservation  of  water  supply  were  undertaken. 
Within  the  past  few  years  remarkable  progress  has  been  made  in 
this  direction.  The  ultimate  limit  of  the  amount  of  land  which  can 
be  brought  under  irrigation  in  the  arid  west  depends  largely  upon 
the  further  conservation  and  storage  of  water  supply  and  improved 
methods  of  transporting,  and  applying  it  to  the  soil. 

Needs  and  Benefits. — The  need  of  irrigation  arises  from  lack  of 
natural  rainfall  at  the  times  when  required  by  crops.  In  some 
regions  the  total  precipitation  annually  is  apparently  adequate  for 
all  vegetation,  but  frequently  the  rain  occurs  at  seasons  when  it  is 
not  needed  and  fails  at  critical  times,  thus  irrigation  must  be  prac- 
tised during  the  season  of  summer  drought.  Under  these  conditions 
it  may  be  considered  as  a  form  of  insurance,  while  in  the  truly  arid 
areas  it  is  an  absolute  necessity. 

The  benefits  which  are  derived  from  irrigation  are  those  which 
arise  from  the  ability  to  supply  the  amount  of  water  needed  by  the 
growing  plants  in  the  quantity  and  at  the  times  when  it  is  most  bene- 
ficial in  crop  production.  In  the  arid  or  dry  regions  where  rainfall 
is  irregular  or  spasmodic  there  are  consequently  few  clouds,  the  sun- 
shine reaches  the  soil  without  obstruction  and  where  water  can  be 
supplied  this  continuous  unobstructed  daily  sunshine  stimulates 
plant  growth  to  a  high  degree,  because  of  the  well-known  fact  that 
all  life  and  growth  on  the  earth  is  maintained  by  the  sun's  energy. 

Irrigation  affords  ideal  conditions  for  agriculture,  since  with  the 
life-giving  sunlight  and  a  means  to  supply  moisture  at  proper  times 
and  in  the  exact  quantity  needed,  agriculture  can  be  reduced  more 
nearly  to  scientific  accuracy. 

It  is  largely  because  of  these  facts  that  agriculture  in  an  arid 
region  offers  larger  opportunities  for  returns  from  a  given  area  than 
in  the  humid  regions,  where  dependence  must  be  placed  upon  an 
erratic  rainfall.  The  amount  of  sunlight  in  the  humid  areas  and 
consequently  the  forces  leading  to  growth  are  limited  by  the  many 
cloudy  days.  Ignoring  this  fact,  it  has  sometimes  been  urged  that 
the  same  amount  of  energy  and  investment  put  in  the  agricultural 
operations  of  the  eastern  part  of  the  United  States  should  be  equally 
or  more  productive  than  in  the  western,  but,  in  this  statement, 
there  is  a  neglect  of  consideration  of  this  all-important  item  of  total 
amount  of  sunlight. 

Methods  of  Irrigation.— Ordinarily,  water  for  irrigation  purposes 


PLATE  I 


FIG.  A. — Diverting  dam  in  Boise  River,  Idaho,  a  typical  structure  for  taking 
out  river  water  by  gravity. 


FIG.  B. — Main  northside  canal  of  Minidoka  Project,  Idaho.     Illustrative  of  the 
larger  irrigation  canals,  with  power  transmission  lines  located  on  the  bank. 

(  Facing  Page  4) 


PLATE  I 


FIG.  C. — Water  being  distributed  to   the  fields  through  furrows  after  having 
been  diverted  from  the  river  by  gravity  canals. 


FIG.  D. — Water  being  applied  to  the  fields  by  flooding. 


IRRIGATION  5 

is  conducted  from  some  stream  or  lake  by  means  of  open  canals  dug 
in  the  rocks  or  earth,  similar  in  many  respects  to  the  drainage  ditches 
commonly  used  in  humid  regions.  In  fact,  the  resemblance  between 
the  irrigation  canal  and  a  drainage  ditch  is  so  great  that  the  word 
" ditch"  is  commonly  applied  to  the  small  irrigating  canal,  although 
it  is  preferable  to  limit  the  word  "ditch"  to  its  original  application 
in  drainage. 

The  main  canal,  designated  to  bring  water  to  a  given  area,  heads 
usually  in  some  perennial  stream  and  takes  water  from  it  either  by 
means  of  a  dam  or  obstruction  in  the  river,  forcing  some  of  the  water 
into  the  canal  (see  Plate  I,  Fig.  A)  or  the  water  is  diverted  by  build- 
ing the  inlet  gates  at  a  level  sufficiently  low  to  permit  it  to  flow  from 
the  stream  into  the  head  of  the  canal.  From  this  point  the  canal  is 
built  on  a  gently  descending  grade  less  than  that  of  the  stream  from 
which  a  supply  is  derived,  that  is  to  say,  if  the  stream  falls  at  a  rate 
of  10  ft.  per  mile,  the  irrigating  canal  may  be  built  with  a  fall  say  i  ft. 
per  mile  and  at  the  end  of  10  miles  the  canal  will  be  90  ft.  above  the 
bed  of  the  stream.  To  build  such  a  canal  in  ground  which  will  sus- 
tain it,  the  canal  after  bordering  the  stream  for  a  short  distance 
must  turn  from  it,  skirting  the  valley  and  thus  partly  surrounding 
a  considerable  body  of  land  which  becomes  wider  and  wider  between 
the  canal  and  the  river.  Water  released  from  the  canal  will  flow 
down  the  natural  drainage  lines  back  to  the  river,  or  it  can  be  kept 
up  on  the  higher  ridges  and  thus  brought  to  the  highest  points  of 
most  of  the  farms  between  it  and  the  river. 

The  canal  divides  or  sends  off  branches  and  these  again  send  from 
their  sides  other  smaller  branches,  sometimes  called  laterals,  dividing 
and  the  sub-dividing  until  each  farm  is  reached.  (See  Plate  I,  Figs. 
C  and  D.) 

Earthen  canals  necessarily  lose  a  considerable  amount  of  water  by 
percolation  or  seepage  into  the  soil,  especially  if  this  is  sandy  or 
gravelly.  There  are  also  small  losses  by  evaporation  from  the  sur- 
face. Where  water  is  very  valuable  the  loss  by  percolation  is  fre- 
quently reduced  by  lining  the  canals  with  masonry  or  other  imper- 
vious materials,  or  by  confining  the  water  in  pipes  as  is  the  case  of 
city  supply. 

Water  having  been  brought  to  the  area  to  be  irrigated,  there  are 
a  variety  of  ways  in  which  it  is  applied  to  the  land.  One  of  the  com- 
mon methods,  ordinarily  known  as  "flooding,"  is  to  deliver  the  water 
to  the  highest  portion  of  the  land  and  allow  it  to  flow  downward 
over  the  slope  until  the  entire  area  or  field  to  be  irrigated  has  been 


6          PRINCIPLES  OF  IRRIGATION  ENGINEERING 

covered.  (Plate  I,  Fig.  D.)  Another  method,  sometimes  called  the 
"check  system,"  requires  that  the  land  be  divided  into  small  areas, 
each  surrounded  by  a  check  or  border  of  earth  a  few  inches  in  height. 
Water  is  turned  into  each  of  the  small  areas  until  it  is  covered  to  the 
required  depth.  This  method  has  advantages  over  ordinary  flood- 
ing in  that  the  amount  of  water  applied  to  each  portion  of  the  land 
can  be  more  accurately  controlled.  In  the  "furrow  system,"  water 
is  carried  over  the  land  in  small  furrows  (Plate  I,  Fig.  C),  excavated 
by  means  of  a  plow  or  other  suitable  appliance,  a  few  feet  apart  over 
the  entire  area.  Still  another  method,  known  as  "sub-irrigation," 
consists  in  bringing  the  water  below  the  surface  by  means  of  pipes 
laid  in  the  soil  and  allowing  it  to  escape  through  small  openings  in 
the  walls  of  the  pipes.  This  method,  while  theoretically  nearly 
perfect,  is  ordinarily  prevented  by  the  excessive  cost. 

Comparison  of  Irrigated  and  Non-irrigated  Lands. — The  advant- 
ages of  irrigation  are  best  expressed  in  values  of  crops  per  acre  on 
irrigated  and  non-irrigated  areas.  Unfortunately  it  is  difficult  to 
make  a  comparison  of  this  kind  on  account  of  the  lack  of  comparable 
data  relative  to  crop  values  in  different  sections  of  the  country. 
There  are  examples  where  special  crops  grown  without  irrigation 
have  yielded  greater  returns  per  acre  then  other  crops  grown  with 
irrigation.  There  are  few  if  any  examples,  however,  where  non- 
irrigated  orchards  have  been  known  to  produce  crop  returns  equal 
to  those  under  irrigation.  The  same  may  also  be  said  of  the  more 
staple  farm  crops  and  especially  is  it  true  for  vegetables  and  what  is 
known  as  truck  farming. 

In  general,  it  is  believed  that  in  a  well-irrigated  region  the  values 
of  ordinary  farm  crops  are  from  50  to  75  per  cent,  greater  than  in 
an  equally  well-farmed  section  of  the  humid  region.  Evidence  of 
this  fact  is  shown  by  the  relative  land  values  upon  which  the  crops 
are  made  to  pay  returns,  and  the  size  of  farms  required  to  support 
a  family. 

The  difference  in  value  is  particularly  marked  in  the  case  of  the 
more  valuable  fruits  because  of  the  fact  that  with  complete  regula- 
tion of  the  water  supply  the  size  and  quality  of  the  fruit  may  be  more 
closely  controlled.  This  same  condition  applies  also,  but  possibly 
in  a  somewhat  less  degree,  to  the  growing  of  forage,  vegetables  and 
other  staple  crops.  Irrigation  consequently  offers  possibilities  of 
intensive  argiculture  and  of  dense  population,  such  as  is  not  practi- 
cable where  dependence  for  a  water  supply  must  be  placed  upon 
rainfall. 


IRRIGATION  7 

In  making  a  comparison  of  the  values  of  products  from  an  irri- 
gated and  non-irrigated  region,  it  must  be  assumed  that  equal  skill 
and  energy  is  involved  and  that  the  cost  of  labor,  means  of  transpor- 
tation and  character  of  markets  are  approximately  the  same.  Even 
with  this  assumption,  which  is  in  many  cases  less  favorable  to  the 
irrigated  areas,  they  generally  show  larger  average  crop  returns. 

It  is  frequently  the  case  that  farmers  practising  irrigation  are 
doing  so  without  the  long  experience  which  has  been  had  in  the  humid 
regions.  Most  of  them  have  come  from  regions  where  dependence 
is  placed  in  rainfall  and  many  of  them  must  unlearn  the  practices 
laboriously  acquired  and  handed  down  for  generations  in  order  to 
make  a  success  of  irrigation  farming.  Others  are  men  with  but 
limited  experience  in  agriculture  who  must  pay  for  the  experience 
they  acquire  by  occasional  failure. 

Irrigation  in  many  parts  of  the  United  States  is  still  in  a  pioneer 
condition  so  that  the  averages  of  productions  are  not  fairly  compa- 
rable with  those  from  the  older  humid  regions.  This  is  in  part  on 
account  of  the  soil  not  being  fully  subdued  and  brought  to  the  point 
where  large  crop  returns  can  be  expected,  and  partly  on  account  of 
the  lack  of  means  by  the  settlers  to  carry  on  operations  in  the  most 
efficient  manner. 


CHAPTER  II 
IRRIGABLE  LANDS 

Arid  Region. — In  the  arid  regions  are  the  best  and  largest  ex- 
amples of  irrigation,  as  here  it  is  a  necessity,  while  elsewhere  it  is 
more  of  the  nature  of  an  insurance  for  crops.  The  arid  regions  of 
the  United  States  are  part  of  those  of  the  North  American  Con- 
tinent which  extend  from  about  Central  Mexico  northerly  in  a 
widening  belt  across  the  United  States  and  into  Canada.  They  are 
generally  defined  as  the  localities  having  less  than  15  inches  of 
annual  rainfall.  They  consist  for  the  most  part  of  elevated  plateaus 
or  broad  valleys  broken  by  mountain  ranges,  the  higher  slopes  of 
which  have  a  humid  climate.  Thus  the  arid  regions  are  not  contin- 
uous, but  are  interspersed  with  areas  of  humidity,  from  which  come 
the  streams  so  essential  in  irrigation  development. 

Aridity  is  a  consequence  of  the  continental  structure  and  is  a 
resultant  of  the  atmospheric  circulation  of  the  globe,  which  cannot 
be  controlled  or  modified  in  any  appreciable  degree  by  the  work  of 
mankind.  It  has  been  the  dream  of  all  the  ages  that  mankind  might 
influence  the  distribution  and  quantity  of  rainfall,  primarily  by 
occult  or  supernatural  agencies,  by  incantations  and  various  cere- 
monies. The  later  manifestations  of  this  hope  have  been  in  the 
efforts  to  bombard  the  heavens,  and  by  concussions  resulting  from 
great  explosions  to  bring  about  the  production  of  rain.  It  has 
also  been  hoped  from  a  more  rational  standpoint  to  modify  the 
quantity  of  precipitation  by  preserving  or  increasing  the  forest 
cover  on  the  uplands.  All  of  these  have  failed,  and  there  is  now  a 
more  general  recognition  of  the  fact,  as  before  stated,  that  the 
formation  of  rain  is  due  to  world- wide  rather  than  to  local  conditions. 

Roughly  speaking,  it  may  be  stated  that  the  arid  regions  of  the 
United  States  lie  from  about  io2nd  meridian  west  of  Greenwich,  or 
about  the  western  limit  of  Kansas,  westerly  to  the  Pacific  Coast, 
in  southern  California,  and  to  the  Cascade  Ranges  of  northern 
California,  Oregon  and  Washington.  To  the  west  of  these,  the 
humidity  is  great  and  it  thus  happens  that  in  the  state  of  Washing- 
ton there  is  extreme  aridity  on  the  east  of  the  mountains  and  equally 
extreme  humidity  to  the  west  of  them. 

8 


IRRIGABLE  LANDS 


9 


As  before  stated,  there  are  scattered  through  this  vast  arid  region 
considerable  areas  of  relatively  humid  mountain  masses,  especially 
in  northern  portion  of  western  Montana  and  in  northern  Idaho. 
The  relative  position  and  extent  of  the  arid,  semi-arid  and  humid 
regions  of  the  United  States  are  shown  in  Fig.  2. 

To  the  east  of  the  truly  arid  region  is  a  broad  belt  of  country,  several 
hundred  miles  in  width,  with  progressive  decrease  from  the  extreme 
aridity  of  the  high  plains  to  the  moderately  humid  conditions  of 
the  lands  of  the  Mississippi  Valley.  This  broad  belt  is  by  no  means 
fixed,  as  in  some  seasons  when  the  rainfall  is  deficient,  the  arid  or 


7 — U       /     »    1 


FIG.  2. — Map  showing  relative  area  and  position  of  arid,  semi- arid  and  humid 
regions  of  the  United  States. 

semi-arid  conditions  progress  to  the  eastward  and  again  retreat 
with  the  non-periodic  fluctuations  or  successions  of  wetter  seasons. 
Thus  there  is  a  broad  belt  of  country  of  which  western  Kansas  is 
typical,  having  a  soil  of  exceptional  fertility,  one  which  has  not 
been  washed  by  the  rains,  but  which  has  alternately  a  climate  too 
dry  for  successful  production  of  ordinary  crops,  followed  by  years  of 
conditions  highly  favorable  for  profitable  agriculture.  These  are 
the  conditions  which  lead  to  what  is  sometimes  known  as  the  famine 
regions  of  the  world,  where  the  richness  of  the  soil  tempts  agricul- 
ture, and  where  successive  years  of  moderate  precipitation  en- 
courages the  development  of  population  to  be  followed  by  dry  years 
with  resulting  poverty  and  suffering. 


10        PRINCIPLES  OF  IRRIGATION  ENGINEERING 

Topographic  Features. — The  arid  region  of  the  United  States  as  a 
whole  is  relatively  high,  including  as  it  does  the  great  plateau  of 
the  Rocky  Mountains  or  Cordilleran  area.  The  general  slope  from 
about  the  center  of  the  region  toward  the  south  is  such  as  to  bring 
the  arid  lands  down  to  or  even  below  sea  level,  as  in  the  case  of  Death 
Valley  and  the  Salton  Desert  in  southern  California.  Toward  the 
north  there  is  also  a  general  decline  in  altitude,  but  far  less  marked 
than  toward  the  south.  The  climate  of  the  northern  portion  of 
this  arid  region  is  modified  and  less  rigorous  on  account  of  this  de- 
scent toward  sea  level. 

The  mountain  masses  which  traverse  the  arid  regions  serve  to 
force  upward  the  prevailing  winds,  causing  them  to  deposit  their 
moisture  on  the  slopes.  These  have  a  relatively  heavy  precipitation 
as  testified  by  the  presence  of  the  forests  which  extend  from  the 
timber  line  well  down  the  sides  toward  the  dry  valleys.  These 
forests  for  the  most  part  have  been  segregated  from  the  public 
domain  of  the  United  States  and  set  aside  as  reservations  or  National 
Forests  (see  Fig.  3)  under  the  charge  of  the  Forest  Service  of  the 
Department  of  Agriculture.  The  primary  object  of  creating  these 
reserves  has  been  for  the  protection  of  the  timber  supply  of  the  coun- 
try, but  a  secondary  and  sometimes  more  important  object  to  be 
attained  is  the  beneficial  effect  which  forest  cover  has  on  the  water 
supply  so  necessary  for  agricultural  development  in  the  valleys. 

These  scattered  mountain  ranges  and  isolated  peaks,  thus  give 
rise  to  innumerable  streams,  some  of  considerable  size.  These 
coming  with  steep  slopes  toward  the  valleys  render  the  conditions 
favorable  for  economical  development  of  irrigation.  In  Utah,  for 
example,  the  almost  innumerable  small  streams  from  the  Wasatch 
Mountains  issuing  upon  the  desert  valleys  at  frequent  intervals, 
enabled  the  pioneers  to  build  their  small  irrigation  canals  at  the 
minimum  of  cost.  Relatively  few  large  structures  were  required 
and  the  steep  slopes  permitted  the  water  to  be  carried  out  in  narrow 
channels  but  still  at  a  sufficient  elevation  to  cover  the  irrigable  lands 
in  the  valleys  below. 

The  Soil. — The  soil  of  the  arid  regions  differs  essentially  from  that 
of  the  humid  regions  in  that  disintegration  has  taken  place  under 
conditions  where  the  earthy  salts  have  not  been  so  completely 
leached  out.  Many  of  the  soils  have  been  built  up  by  wind  action, 
others  are  alluvial  or  delta  deposits  brought  out  upon  the  margin 
of  the  valleys  by  the  streams  issuing  from  the  high  mountains. 
Still  others  have  resulted  from  sedimentation  in  fresh-water  lakes. 


IRRIGABLE  LANDS 


11 


12        PRINCIPLES  OF  IRRIGATION  ENGINEERING 

As  a  whole,  the  soils  are  more  highly  productive  in  their  natural 
condition  than  those  of  the  humid  regions,  excepting  possibly  those 
of  the  swamp  lands. 

One  of  the  most  notable  characteristics  of  the  agricultural  soils 
of  the  arid  region  is  the  deficiency  of  organic  vegetable  matter.  The 
first  effort  of  the  skilled  irrigation  farmer  is  to  supply  this  lack. 
Fortunately,  alfalfa,  one  of  the  most  valuable  of  the  forage  plants, 
is  also  valuable  for  supplying  organic  matter  to  the  soil.  This 
plant  also  has  the  property  of  obtaining  nitrogen  from  the  air,  and 
giving  it  to  the  soil,  through  the  activities  of  bacteria  which  inhabit 
nodules  on  the  roots.  As  soon,  therefore,  as  the  soil  has  been  broken 
up  and  partly  subdued  by  planting  a  grain  or  similar  crop,  alfalfa 
is  put  in  and  after  a  few  cuttings  the  green  plants  are  plowed  under, 
thus  supplying  the  soil  with  the  necessary  organic  matter,  and  mak- 
ing it  capable  of  producing  subsequently  large  crops  of  potatoes, 
sugar  beets,  or  other  vegetables. 

Preparation  of  Lands. — The  first  and  most  important  step  in 
preparing  the  lands  for  irrigation  is  to  smooth  and  level  the  surface 
as  accurately  as  possible.  If  this  is  once  properly  done,  it  will  be 
possible  to  till  the  soil  year  after  year,  and  apply  water  with  a  mini- 
mum amount  of  labor  and  loss.  If  it  is  not  carefully  performed 
there  will  always  be  difficulty  in  thorough  irrigation  with  resulting 
uneven  growth  of  plants  due  to  the  fact  that  water  has  been  applied 
more  plentifully  in  some  spots  than  in  others. 

In  its  native  state,  most  of  the  best  agricultural  land  is  covered 
with  sagebrush.  Other  lands  have  the  so-called  greasewood  or 
similar  desert  vegetation,  nearly  all  of  which  is  easily  removed  by 
dragging  with  a  heavy  iron  bar  or  by  using  heavy  machines  made 
especially  for  the  purpose.  Having  removed  the  sagebrush,  the  next 
step  is  to  break  up  the  ground  with  a  plow,  and  then,  as  above  stated, 
to  smooth  and  level  it  into  small  fields  or  "lands,"  using  for  this 
purpose  a  scraper  or  drag  by  which  the  higher  knolls  are  shaved  off 
and  the  depressions  filled. 

Where  heavy  winds  prevail,  especially  in  the  spring,  particular 
care  must  be  taken  not  to  remove  at  once  all  of  the  sagebrush  or 
other  desert  vegetation,  because  by  so  doing  the  winds  have  access 
to  the  loose  soil  and  readily  blow  it  away,  cutting  out  the  seed  or 
young  plants.  By  leaving  rows  of  sagebrush  across  the  path  of  the 
wind  and  cultivating  the  intervening  strips,  the  surface  is  protected 
until  the  plants  thoroughly  shade  the  ground;  it  is  then  possible  to 
take  out  the  windbreaks  and  cultivate  the  remaining  soil.  By  the 


IRRIGABLE  LANDS  13 

exercise  of  skill  and  forethought  it  is  thus  possible  to  get  into  crop 
lands  which  otherwise  could  not  be  handled.  After  the  first  few 
years  of  cultivation,  especially  after  a  certain  amount  of  vegetable 
matter  is  gotten  into  the  ground,  the  tendency  of  the  soil  to  be  moved 
by  the  wind  is  greatly  decreased  and  by  planting  trees  for  windbreaks 
and  taking  other  precautions,  the  difficulties  encountered  by  the 
pioneers  are  successfully  overcome. 

Location. — There  is  more  land  than  water  with  which  to  irrigate 
in  most  parts  of  the  arid  region.  For  a  given  water  supply  there  is 
usually  possible  a  choice  of  lands  not  merely  with  reference  to  physical 
characteristics  but  with  regard  to  accessibility  to  markets  or  lines 
of  communication.  The  arid  region,  as  a  whole,  is  sparsely  popu- 
lated, there  being  few  notable  cities,  but  with  the  development  of 
the  railroad  systems,  it  is  now  possible  to  reach  nearly  all  the  irrigable 
lands  with  relatively  short  wagon  roads.  Much  of  the  success  of 
any  irrigation  project  depends  upon  the  choice  of  lands  in  such  way 
that  the  distance  to  markets  and  cost  of  transportation  will  be  as 
small  as  possible. 

The  west  is  favored  in  the  fact  that  the  precious  minerals  are  quite 
widely  disseminated  and  at  the  mining  camps  there  is  usually  an 
excellent  market  for  everything  which  can  be  raised  under  irrigation. 
In  fact  the  two  occupations  are  interdependent  in  that  the  develop- 
ment of  agriculture  in  the  vicinity  reduces  the  cost  of  living  and 
consequently  the  cost  of  mining,  so  that  the  lower-grade  ores  can  be 
handled  and  the  development  of  these  mines  gives  a  needed  market 
for  the  crops. 

Intensive  Farming. — The  large  amount  and  intensity  of  degree  of 
the  sunlight  and  favorable  condition  of  soil  as  compared  with  the 
humid  regions  render  it  possible  for  the  average  farmer  to  be  sup- 
ported on  a  much  smaller  tract  of  land  than  is  the  case  in  the  non- 
irrigated  portions  of  the  United  States.  The  expense  of  building  long 
lines  of  canals  results  also  in  bringing  the  farms  close  together  and 
in  utilizing  to  the  fullest  extent  possible  all  the  lands  within  a  given 
district.  The  irrigated  areas  are  not  only  capable  of  the  most 
intensive  cultivation  but  all  of  the  conditions  of  water  supply  and  of 
transportation  favor  the  most  complete  development. 

The  high  price  of  labor  which  prevails  through  the  western  part  of 
the  United  States  results  in  the  greater  part  of  the  work  on  each  farm 
being  performed  by  the  family  living  upon  it,  and  this  in  turn  tends 
to  keep  down  the  area  of  each  farm  and  increase  the  economics  and 
the  product  per  acre.  As  time  goes  on,  with  greater  increased  ca- 


14        PRINCIPLES  OF  IRRIGATION  ENGINEERING 

pacity  for  production  and  with  growth  of  population,  the  farms  are 
further  sub-divided;  there  is  a  marked  tendency  toward  still  more 
intensive  cultivation  and  with  corresponding  increase  in  values  the 
occupation  of  smaller  and  smaller  areas  per  family,  the  standard  of 
living  increasing  with  the  higher  productivity  of  soil. 

Climate. — The  climatic  conditions  are  those  generally  known  as 
continental  and  are  correspondingly  extreme  with  cold  winters  and 
hot  summers.  The  dryness  of  the  air  renders  these  extremes  of  tem- 
perature less  burdensome  than  they  would  be  in  more  humid  portions 
of  the  country.  The  summers,  with  their  continuous  daily  sunshine, 
even  though  relatively  short  in  the  north,  are  conducive  to  large  crop 
production.  In  the  southern  portion  of  the  arid  regions,  for  example 
in  Arizona,  crop  growth  continues  practically  throughout  the  year, 
there  being  hardly  a  perceptible  rest  of  plant  activity  during  the 
winter,  so  that  crop  follows  crop  in  succession  as  rapidly  as  it  can  be 
matured  and  removed.  As  far  as  human  health  is  concerned  and 
that  of  domestic  animals,  the  extreme  aridity  seems  to  be  highly 
beneficial  and  is  in  general  recommended. 


CHAPTER  III 
WATER  SUPPLY 

Source  of  Water  Supply. — The  principal  source  of  water  supply  for 
irrigation  is  from  the  perennial  streams  which  issue  from  the  higher 
mountains.  A  relatively  small  but  increasingly  important  amount 
of  water  is  derived  from  floods  which  are  held  in  reservoirs  and  a  still 
smaller  proportion  from  natural  storage  in  the  ground,  the  water 
being  recovered  by  wells  sunk  in  the  gravels  or  sands  of  the  valleys. 

The  streams  which  have  their  source  in  the  high  mountains  are 
maintained  not  only  by  the  rainfall  on  the  mountain  sides  but  are 
increased  in  volume  by  the  melting  snows.  With  their  large  supply 
from  the  forested  areas  they  are  the  most  nearly  ideal  for  purposes  of 
irrigation.  The  annual  floods  occur  at  a  nearly  definite  date  and  it  is 
possible  to  plant  crops  with  reasonable  assurance  of  an  adequate 
amount  of  water  for  ordinary  irrigation.  These  are  the  sources  of 
supply  which  have  been  first  utilized  and  which  are  now  in  many 
instances  over-appropriated,  that  is  to  say,  the  claims-for  use  of  water 
aggregate  more  than  the  usual  flow. 

In  distinction  from  mountain  streams  are  those  which  have  a  less 
elevated  catchment  area,  and  which  depend  for  water  upon  the  less 
regular  rainfall.  These  are  occasionally  in  flood  but  for  the  greater 
part  of  the  year  are  nearly  or  quite  dry  and  cannot  be  depended  upon. 
Irrigation  has  been  tried  along  these  streams  and  considerable  in- 
vestment made  but  with  little  success,  as  the  headworks  are  fre- 
quently washed  out  by  the  erratic  floods,  and  before  they  can  be 
restored  the  stream  has  usually  gone  dry.  In  nearly  every  case  it  is 
necessary  to  provide,  wherever  possible,  large  and  expensive  reser- 
voirs out  on  the  plains  in  order  to  regulate  the  supply.  Even  then 
there  is  considerable  uncertainty  owing  to  the  fact  that  the  rainfall 
in  these  lower  regions  is  not  as  uniformly  distributed  as  it  is  on  the 
higher  summits. 

Character  of  Supply. — From  what  has  been  stated,  it  is  apparent 
that  there  is  a  very  great  difference  in  the  amount  and  reliability 
of  supply  to  be  had  from  different  streams.  Those  coming  from  the 
mountains  with  forested  and  lofty  catchment  areas  afford  the  fewest 

15 


10       PRINCIPLES  Ob'  IRRIGATION  ENGINEERING 

problems,  as  their  flow  is  relatively  steady,  while  those  coming  from 
lower  and  more  open  regions  offer  increasingly  difficult  questions, 
and  necessitate  the  careful  study  of  all  opportunities  for  providing 
storage  reservoirs. 

The  accompanying  diagrams,  Fig.  4  and  Fig.  5,  illustrate  the  differ- 
ence in  behavior  of  typical  rivers  of  the  eastern  humid  part  of  the 
United  States,  and  of  the  western  arid  portion.  In  Fig.  4  is  indicated 
by  the  position  and  height  of  the  black  areas  the  relative  quantity 
of  water  expressed  in  cubic  feet  per  second  or  second-feet,  occurring 
throughout  the  year.  The  diagram  illustrates  the  fact  that  the 
greater  portion  of  the  water  in  the  Susquehanna  River  at  Harrisburg, 
Pa.,  occurs  in  the  spring,  with  summer  drought,  most  notable  in  the 
latter  part  of  August,  and  early  in  September.  In  the  case  of  the 
Yadkin  River  at  Salisbury,  N.  C.,  the  greater  portion  of  the  water 
occurred  in  short  quick  floods  in  the  latter  part  of  the  summer  and 
early  in  the  autumn,  these  being  the  result  presumably  of  heavy 
storms  on  the  mountains. 

In  comparison  with  this  is  the  diagram  for  the  Gila  River  at 
Buttes,  Ariz.,  showing  a  very  small  relatively  steady  flow  during  the 
early  part  of  the  year  followed  by  erratic  floods  due  to  so-called 
" cloud  bursts"  on  the  drainage  basin.  In  marked  contrast  to  this 
is  the  large  comparatively  uniform  flood  in  the  Green  River  at  Blake, 
Utah,  typical  of  the  streams  which  come  from  the  snow-clad  moun- 
tains, the  water  being  supplied  by  the  melting  of  the  snow  as  sum- 
mer advances. 

A  record  of  the  behavior  of  the  streams  of  the  arid  region,  as  well 
as  those  of  the  humid  region,  has  been  undertaken  by  the  United 
States  Geological  Survey  and  beginning  in  about  1888,  systematic 
observations  have  been  conducted  on  many  rivers  and  creeks.  It 
has  not  been  possible  to  measure  all  of  the  flowing  waters,  but  the 
attempt  has  been  made  to  select  typical  streams  which  would  be 
fairly  representative  of  others  in  the  vicinity. 

The  height  of  water  at  selected  points  has  been  observed  and  re- 
corded day  by  day,  and  the  quantity  of  flow  corresponding  to  the 
various  heights  has  been  ascertained.  By  means  of  these  data  it  has 
been  possible  to  compute  the  total  flow  at  the  observed  points  by 
months  and  seasons,  giving  figures  of  the  amount  and  duration  of 
floods  and  of  the  low-water  periods. 

Benefits  of  Control. — The  benefits  which  arise  from  the  ability 
to  store  these  flood  or  waste  waters  need  hardly  be  enumerated. 
These  waters  unregulated  frequently  occur  in  quantity  sufficient  to 


WATER  SUPPLY 


17 


1 1  §  1 1 1 1  . 1 1  i  § 

-  - 


i  1 1  i  i  i  §  i 
gftiaaaaafaa 


I  I  I  I 


I 

q 


18        PRINCIPLES  OF  IRRIGATION  ENGINEERING 

destroy  bridges,  dams  and  other  structures  along  their  course  or  to 
overflow  the  farms  and  villages  on  the  lowlands.  By  holding  back  the 
floods,  which  if  unregulated  would  be  a  source  of  destruction,  it  is 
possible  to  use  this  water  in  the  reclamation  of  waste  and  useless 
land  and  thus  provide  opportunities  for  citizens  and  their  familiers 
who  otherwise  would  not  be  able  to  obtain  a  foothold  on  the  land. 
From  the  standpoint  of  the  stability  of  the  commonwealth,  there  is 
perhaps  no  engineering  or  economic  operation  which  has  a  deeper 
significance  or  is  of  greater  value  than  this  practical  application  of 
the  principles  of  conservation. 

By  a  study  of  the  data  obtained  from  systematic  measurements 
it  has  been  possible  to  arrive  at  certain  conclusions  with  reference 
to  the  practicability  of  conserving  the  waste  waters  and  holding 
them  wherever  suitable  natural  basins  can  be  found,  the  outlet 
of  which  may  be  closed  by  dams  at  reasonable  cost.  The  Federal 
Government,  as  the  original  proprietor  and  still  the  owner  of  vast 
tracts  of  desert  land,  is  interested  in  obtaining  all  of  these  facts 
upon  which  engineering  operations  may  be  based  and  by  which 
money  may  be  safely  invested  in  the  construction  of  storage  works 
for  holding  the  flood  waters  and  for  delivering  them  at  the  proper 
time  to  the  lands  which  may  be  irrigated. 

Study  of  Water  Supply. — In  the  study  of  the  water  supply  and 
the  practicability  of  storing  or  diverting  it,  the  principal  features  of 
importance  are  the  daily  or  periodic  observations  of  quantities. 
From  these  a  great  variety  of  facts  relative  to  the  amount  of  water 
available  from  a  given  stream  may  be  secured  and  comparisons 
made.  At  the  same  time  it  is  important  to  obtain  definite  knowledge 
concerning  the  topography  of  the  catchment  area  from  which  the 
water  flows,  and  to  know  its  cultural  conditions,  and  whether  these 
are  likely  to  be  changed  in  such  way  as  to  modify  the  amount  of 
water  available.  One  of  the  important  factors  in  a  water  supply  is 
its  constancy  or  regularity  of  flow.  In  order  to  determine  this  it  is 
necessary  to  have  records  extending  over  a  period  of  years. 

In  choosing  a  water  supply,  preference  should  be  given  to  one 
which  is  constant  in  character  rather  tnan  one  which  varies  greatly 
from  year  to  year,  even  though  the  total  flow  from  the  constant 
source  is  somewhat  the  smaller. 

Rainfall. — The  primary  factor  in  questions  of  water  supply  is  the 
amount  of  precipitation  in  the  form  of  rain  or  snow  which  reaches 
the  earth.  This  varies  greatly  in  different  parts  of  the  country, 
being  governed  quite  largely  by  geographic  or  topographic  relations. 


WATER  SUPPLY 


19 


Without  entering  into  detailed  discussion  of  these,  it  is  sufficient  to 
call  attention  to  the  result  as  illustrated  by  the  accompanying  map 
(Fig.  6),  showing  that  there  is  a  wide  divergence  in  the  total  quantity 
of  precipitation  in  different  parts  of  the  United  States,  the  greatest 
rainfall  being  on  the  eastern  coast  and  near  the  Gulf  of  Mexico  and, 
on  a  comparatively  narrow  strip  of  country  adjacent  to  the  Pacific 
Ocean  in  the  extreme  Northwest.  The  least  amount  of  rain  which 
occurs  is  that  within  the  interior  of  the  country  which  includes  a 
considerable  portion  of  what  now  forms  the  states  of  Nevada,  Utah, 
New  Mexico,  Arizona,  and  adjacent  portions  of  California. 


FIG.  6. — Map  showing  mean  annual  rainfall  of  the  United  States. 

The  above  map  shows  in  a  general  way  the  inequalities  of  distribu- 
tion throughout  the  surface  of  the  country  being  the  averages  of 
observations  carried -on  ,  through  many  years.  For  any  single 
locality  there  is  great  divergence;  during  one  year  there  may  occur 
nearly  twice  as  much  rainfall  as  during  some  preceding  or  succeeding 
year.  This  is  illustrated  by  the  diagram  Fig.  7  of  the  annual  pre- 
cipitation at  Salt  Lake  City,  Utah,  where  the  average  is  about  16 
inches,  with  few  years  which  approximate  this  amount. 

Attempts  have  been  made  to  arrive  at  some  rule  or  generalization 
regarding  this  irregularity  of  rainfall;  efforts  have  been  made  to 
connect  it  with  the  occurrence  of  the  sun  spots  and  other  natural 
phenomena.  Various  students  have  figured  out,  to  their  own  satis- 


20        PRINCIPLES  OF  IRRIGATION  ENGINEERING 


faction,  that  years  of  drought  or  flood  occur  with  a  certain  general 
regularity  in  cycles  of  7  years,  or  n  years,  or  17  years,  but  hardly 
any  two  of  these  persons  will  agree  as  to  the  actual  facts  or  conclu- 
sions to  be  drawn  from  them.  For  most  practical  purposes,  atten- 
tion should  be  concentrated  on  the  fact  that  whenever  a  relatively 
dry  year  occurs,  it  may  be  followed  by  an  even  greater  drought  and 
provision  must,  therefore,  be  made  to  meet  a  succession  of  relatively 
dry  years. 


MEAN- 
IS 


1  II 


N<«)o>o^&a> 

Illlilll- 


FIG.  7. — Diagram  of  annual  precipitation  at  Salt  Lake  City,  Utah,  illustrating 
the  fluctuations  in  total  quantity  of  rainfall. 


Runoff.— The    term    "runoff" 
expression  for  the  water  which 


was  devised  as  a  convenient 
flows  off  the  surface  of  the  land 
in  the  form  of  visible  streams.  The  relation  between  the 
amount  of  water  which  falls  upon  the  land  in  the  form  of  rain  or 
snow  and  the  amount  of  runoff  which  may  become  available  for 
irrigation  has  been  a  source  of  investigation  and  controversy  among 
engineers.  The  inference  war,  drawn  by  some  engineers  and  physi- 
cists, from  early  observations  on  rainfall  and  runoff,  that  a  some- 
what definite  relation  existed  between  them  and  that  by  knowing 
the  rainfall  the  amount  of  runoff  could  be  calculated.  The  results 


WATER  SUPPLY  21 

which  have  followed  from  this  theory  have  been  highly  interesting 
but  in  many  cases  widely  at  variance  with  actual  conditions. 

On  certain  of  the  watersheds  in  the  eastern  and  more  humid 
regions  of  the  United  States,  where  the  rainfall  is  relatively  constant 
in  amount  and  time  of  occurrence,  there  seems  to  be  a  relatively 
consistent  ratio  between  the  rainfall  and  runoff.  In  the  arid  west 
this  does  not  appear  to  exist  and  attempts  to  apply  the  ratios  found 
in  the  humid  regions  of  the  east  to  the  arid  regions  of  the  west 
produce  misleading  and,  in  many  cases,  ludicrous  results.  A  case 
illustrating  the  above  remarks  is  that  of  an  engineer  acquainted 
with  eastern  conditions  only  who  was  employed  to  investigate  the 
water  supply  available  from  an  Arizona  river.  By  taking  the  rain- 
fall of  the  area  and  using  what  he  considered  a  conservative  allow- 
ance, namely,  about  20  per  cent,  for  runoff,  he  reached  the  conclusion 
that  a  certain  amount  of  water  would  be  available.  It  so  happened 
that  measurements  had  already  been  made  which  showed  the  runoff 
to  be  a  little  more  than  2  per  cent,  of  the  rainfall.  The  engineer  in 
question  was  very  sure  that  there  must  be  an  error  in  printing 
the  records  of  stream  flow,  since  his  careful  analysis  had  demon- 
strated to  him  that  the  water  which  theoretically  would  be  available 
was  ten  times  that  found  by  direct  observation. 

Influences  affecting  Runoff. — A  clear  conception  of  the  varying 
character  of  runoff  can  be  obtained  by  considering  it  as  the  excess 
of  water  on  a  given  area  after  all  of  nature's  requirements  for 
moisture  on  that  area  have  been  supplied.  It  is  the  balance,  so  to 
speak,  between  nature's  supply  and  immediate  needs.  If  no  more 
water  falls  on  a  given  area  than  can  be  taken  up  and  absorbed  by 
it  the  resulting  runoff  will  be  nil.  The  time  allowed  for  water  to 
be  taken  up  either  through  the  soil  or  the  atmosphere,  as  will  be 
seen  later,  also  plays  an  important  part  in  determining  how  much 
will  be  absorbed  and  how  much  will  be  carried  away  by  streams. 

The  principal  factors  which  affect  directly  the  amount  of  runoff 
are:  amount  and  character  of  rainfall,  character  of  watershed, 
and  evaporation.  All  of  these  are  varying  influences  of  so  com- 
plex a  nature  that  it  is  impossible  to  determine  any  accurate  measure 
of  their  value.  It  is  possible  in  some  cases  to  find  watersheds  where 
conditions  will  give  nearly  the  same  amount  of  runoff  on  each  of 
them.  Where  this  is  the  case,  an  estimate  of  the  runoff  from  an 
unknown  area  may  be  obtained  by  comparing  it  with  that  of  a 
similar  area  where  measurements  have  been  made. 

The  first  and  most  important  consideration  for  runoff  is  rainfall. 


22        PRINCIPLES  OF  IRRIGATION  ENGINEERING 

It  does  not  follow,  however,  that  rainfall  always  produces  runoff. 
It  is  a  significant  fact  that  a  certain  amount  of  rainfall  is  required 
before  any  runoff  will  result.  This  minimum  amount  will  vary  for 
different  watersheds  and  climatic  conditions.  It  is  also  true  that  the 
ratio  of  runoff  to  rainfall  increases  with  the  rainfall.  The  first  ques- 
tion then  is  whether  the  total  rainfall  on  a  given  area  is  sufficient  to 
produce  any  appreciable  runoff.  Granting  that  this  be  the  case,  the 
next  question  is  to  determine  what  amount  of  runoff  may  be  expected. 

If  the  rainfall  occurs  in  heavy,  copious  showers,  so  that  only 
a  small  amount  has  time  to  soak  into  the  soil,  the  greater  part  may 
be  carried  away  over  the  surface  and  eventually  be  collected  in 
the  streams  below.  The  same  amount  of  rainfall  occurring  in  a  slow 
steady  drizzle  may  be  entirely  absorbed  by  the  soil  and  add  nothing 
to  the  stream  flow.  If  precipitation  comes  in  the  form  of  snow  and, 
as  is  frequently  the  case,  is  banked  up  in  the  ravines,  it  may  be  held 
well  into  the  summer  months,  acting  in  the  meantime  to  supplement 
the  stream  flow  at  a  more  or  less  uniform  rate. 

Character  of  Watershed. — The  steepness  of  the  slopes,  kind  and 
depth  of  soil,  and  the  presence,  of  vegetation  upon  a  watershed  will 
influence  in  a  marked  degree  the  amount  of  runoff.  Where  water 
falls  upon  steep  slopes  it  flows  away  rapidly  and  before  a  large 
part  of  it  can  be  absorbed  by  the  soil.  Even  when  the  soil  becomes 
saturated  to  some  depth  through  long-continued  rains  the  steep 
slopes  permit  more  rapid  drainage  and  it  results  that  a  greater 
amount  of  water  is  carried  away  from  them  than  would  be  the  case 
on  flat  slopes  otherwise  similar  in  character.  A  rainfall  giving  as 
high  as  30  or  40  per  cent,  runoff  on  the  steep  sides  of  a  mountain 
range  may  not  produce  more  than  3  or  4  per  cent,  on  the  lower 
level  or  gently  rolling  plains. 

A  deep  porous  soil  will  absorb  and  hold  more  water  than  a  shallow 
compact  one.  On  rock  slopes  practically  no  water  is  lost  by  absorp- 
tion, hence  greater  runoff  results  from  them  than  from  earthen 
slopes.  The  presence  of  frost  in  the  ground  also  tends  to  increase 
the  amount  and  rate  of  runoff. 

The  flow  of  water  is  retarded  if  the  ground  is  covered  by  a  forest 
or  other  form  of  vegetation.  More  water  will  consequently  sink 
into  the  soil  under  these  conditions  than  will  be  the  case  on  land  de- 
void of  vegetation.  The  presence  of  a  forest  cover  also  modifies  the 
rate  of  runoff  by  holding  back  a  part  of  the  waters  and  permitting 
them  to  slowly  trickle  down  to  the  streams.  For  this  reason  it  is  of 
value  in  reducing  the  intensity  of  the  flood  flow  after  severe  storms. 


WATER  SUPPLY  23 

Evaporation. — The  greatest  influence  affecting  runoff  is  evapor- 
ation. Its  action  is  continuous  from  every  part  of  a  watershed 
where  moisture  is  exposed  to  the  atmosphere.  Vegetation,  wherever 
present,  and  capillary  action  in  the  soil  are  constantly  bringing 
moisture  to  the  surface  of  soils  where  it  is  changing  to  vapor.  The 
action  of  evaporation,  while  ordinarily  continuous  in  character, 
nevertheless  varies  greatly  in  amount  at  different  times  and  in  differ- 
ent localities. 

The  rate  of  evaporation  depends  primarily  upon  the  capacity 
of  the  atmosphere  to  take  up  moisture  and  the  ability  of  the  surface 
to  supply  this  moisture  as  rapidly  as  it  can  be  absorbed.  The  capac- 
ity of  the  atmosphere  to  receive  and  dissipate  moisture  depends 
upon  temperature,  rate  of  wind  movement  and  the  degree  of  satura- 
tion or  amount  of  water  which  it  already  contains.  The  rate  at 
which  the  soil  can  supply  moisture  depends  primarily  upon  the  depth 
to  water  and  the  capillary  action  of  the  soil  in  bringing  this  water 
to  the  surface. 

Where  water  stands  on  the  surface  or  where  the  surface  layer  of 
the  soil  is  saturated,  the  earth  can  supply  moisture  at  a  greater  rate 
than  the  air  can  absorb  it.  This  condition  exists  on  the  surface  of 
lakes  and  ponds  and  upon  land  immediately  after  a  rain.  If  the 
surface  supply  is  not  replenished  by  frequent  rains  the  moisture 
disappears  partly  by  seepage  downward  and  partly  by  evaporation 
until  a  condition  exists  where  little  or  no  water  will  be  supplied  to 
the  air.  This  is  frequently  the  case  in  the  extreme  arid  regions. 
The  rate  of  evaporation  for  a  short  period  after  a  storm  may  be  very 
rapid  but  practically  negligible  for  the  remainder  of  the  year.  In  the 
humid  regions,  where  the  surface  of  the  soil  is  moist  during  the  greater 
part  of  the  year,  the  annual  loss  by  evaporation  is  relatively  constant. 

It  is  evident  that  for  a  watershed  from  which  there  is  no  under- 
ground flow,  the  runoff  is  equal  to  total  rainfall  less  evaporation. 
Such  conditions  apply  closely  on  a  large  area  where  the  underground 
losses,  if  any,  from  it  are  so  small  as  to  be  negligible  when  compared 
with  the  total  amount  of  water  which  falls  on  the  area.  On  small 
areas  of  a  few  hundred  square  miles  and  from  which  the  underground 
flow  may  amount  to  several  per  cent,  of  the  rainfall,  it  is  evident 
they  do  not  apply. 

Runoff  on  Different  Watersheds. — As  illustrating  the  difference 
in  amount  of  runoff  from  different  watersheds  in  various  parts  of 
the  United  States,  the  following  table  is  presented.  This  table  has 
been  prepared  from  the  records  of  stream  gagings  made  by  the 
United  States  Geological  Survey: 


24        PRINCIPLES  OF  IRRIGATION  ENGINEERING 


MEAN  ANNUAL  RUNOFF  FOR  VARIOUS  WATERSHEDS  IN  THE  UNITED 

STATES 


River 

Point  of  measurement 

Drainage 
area 
square 
miles 

Period 

Runoff   in 
depth  in 
inches  on 
drainage 
area 

Kern   

Bakersfield,   Cal  

2,340 

1896-1905 

4.36 

Herndon,  Cal 

i  640 

1896—1901 

20.47 

Kings 

Sanger,  Cal       

1,740 

1897-1906 

20.38 

Sacramento  

Red  Bluff,  Cal  

4,300 

1902-1906 

24.06 

LJmatilla 

Umatilla   Ore 

2  130 

Nov    i    1900  to 

3   94 

Dec.  31,  1900 

Willamette 

Albany,  Ore 

4  860 

Jan.  i,  1899   to 

46.62 

Dec.  31,  1908 

Boise 

Boise,  Idaho  

2,610 

1895-1904 

15.60 

Green  

Green  River,  Wyo  

7,450 

May  i,  1896,  to 

4.81 

Oct.   31,    1906 

Laramie  

Uva,  Wyo  

3,180 

May,  1895,  to 
Oct.,  1903 

I  .  IO 

Red 

Grand  Forks,  N.  Dak. 

25,100 

Sept.,  1902,  to 

2.08 

Sept.,  1908 

Rio  Grande  

Rio  Grande,  N.  Mex  

14,000 

Jan.  i,  1896,  to 

1.46 

Dec.  31,  1905 

Durango,  Col. 

812 

July    1895   to 

14  86 

Dec.,  1905 

South  Platte 

Denver,  Col  

3,840 

Jan.  i,  1896,  to 

i  .44 

Nov.  30,  1906 

Green  

Greenriver,  Utah  

38,200 

Jan.,  1895,  to 

3-  17 

Dec.,  1908 

Logan,  Utah       

218 

1896—1900 

21    18 

1904-1906 

088 

6    25 

Dec.,  1906 

Truckee 

Vista,  Nev  

I  520 

Sept     1899   to 

9   18 

Dec.,  1906 

Humbolt  

Orleans,  Nev  

13,800 

Jan.,  1897,  to 

o  25 

Dec.,  1906 

WATER  SUPPLY 


25 


MEAN  ANNUAL  RUNOFF  FOR  VARIOUS  WATERSHEDS  IN  THE  UNITED 
STATES— Continued. 


River 

Point  of  measurement 

Drainage 
area 

square 
miles 

Period 

Runoff  in 
depth  in 
inches  on 
drainage 
area 

225  ooo 

Jan     1902   to 

i   i  ? 

Dec.,  1906 

St    Croix 

St.  Croix  Falls,  Wis      . 

6,370 

1902—1904 

10  60 

Menominee  

Iron  Mountain,  Mich..  . 

2,420 

Sept.,  1902,  to 
Sept.,  1906 

18.92 

Peoria   111 

13  2OO 

Apr    i    1903   to 

14  ii 

Jan.  30,  1906 

Waterville,  Ohio     .    .  . 

6,1  10 

Dec.,  1898,  to 

13.61 

Jan.,  1902 

Scioto  

Columbus,  Ohio  

1,050 

1899  to 
July,  1906 

10.43 

Duck  

Columbia,  Tenn  

1,260 

Nov.  i,  1904,  to 

18.87 

Dec.  31,  1908 

Tennessee       ...    . 

Chattanooga,  Tenn 

21,400 

1899-1908 

23.63 

Tombigbee  

Columbus,  Miss  

4,440 

1905-1908 

15-48 

Black  Warrior 

Cordova  Ala 

I  900 

1900—1908 

19.37 

Alabama 

Selma   Ala.. 

15  400 

1900—1908 

24.01 

Savannah  

Augusta,  Ga  

7,300 

1899—1908 

22.29 

Catawba  

Rock  Hill,  S.  C  

2,990 

1895-1903 

25.21 

Tar 

Tarboro    N.  C 

2  290 

1896—1900 

13.89 

Roanoke     

Randolph,  Va 

3  080 

1901—1905 

18.86 

Potomac  

Pt.  of  Rocks,  Va  

9.650 

1895-1906 

14.40 

Oswego 

Oswego   N.  Y 

5  ooo 

1897—1901 

ii  .69 

Delaware  

Port  Jarvis,  N.  Y  

3.250 

1904-1908 

22.  2O 

Susquehanna  

Binghamton,  N.  Y  

2,400 

1901-1906 

28.88 

Hudson  

Mechanicsville,  N.  Y... 

4.500 

1891-1900 

22.95 

Mohawk  

Dunsbach  Ferry,  N.  Y.  . 

3,440 

1898-1907 

23.28 

26        PRINCIPLES  OF  IRRIGATION  ENGINEERING 

Comparison  of  Runoff. — A  comparison  of  the  runoff  on  different 
watersheds  frequently  leads  to  interesting  conclusions,  especially 
when  the  various  factors  which  influence  it  are  considered.  If  a 
comparison  is  made  without  first  considering  the  amount  and  char- 
acter of  rainfall,  the  nature  of  the  soil,  and  losses  by  evaporation, 
the  results  are  not  only  confusing  but  frequently  lead  to  far-reaching 
engineering  blunders.  For  example,  the  earliest  data  available 
were  from  watersheds  in  New  England  or  New  York.  These  were 
fairly  consistent  among  themselves  and  it  was  possible  to  deduce 
rules  for  local  application  to  the  effect  that  about  30  per  cent,  of  the 
rainfall  might  be  found  in  the  stream.  Engineers  have  some  times 
taken  these  conclusions  and  attempted  to  apply  them  in  the  west, 
with  the  result  that  they  have  been  greatly  misled  in  their  assump- 
tions of  available  water  supply. 

This  has  been  due  not  merely  to  the  fact  that  direct  comparison 
could  not  be  made,  but  also  to  what  should  have  been  even  more 
obvious;  namely,  that  the  measured  rainfall  in  the  west  has  been 
mostly  in  the  valleys  and  rarely  on  the  higher  portions  of  the  catch- 
ment area  from  which  comes  the  greater  part  of  the  water. 

It  is  important  and  necessary  in  some  cases  to  make  deductions, 
based  upon  comparisons  or  runoff  of  various  watersheds,  since  it 
has  not  been  possible  to  measure  the  runoff  from  every  stream. 
When  such  comparisons  are  made,  however,  great  care  must  be 
exercised  in  selecting  areas  which  are  similar  in  character.  It  is 
recognized  that  an  area  of  1,000  square  miles  may  have  a  different 
character  of  runoff  from  one  of  100  square  miles,  even  in  the  same 
region,  so  that  when  it  is  desirable  to  study  the  amount  of  water 
probably  available  from  a  river  basin  of  a  thousand  square  miles, 
it  is  important  to  obtain  the  measurements  which  have  applied  to  a 
similar  area  and  not  to  one  notably  larger  or  smaller. 

It  must  be  recognized  that  conclusions  drawn  from  such  compari- 
sons are  at  best  subject  to  grave  error,  and  that  an  accurate  value 
of  runoff  can  be  had  only  by  direct  measurement. 

Measurement  of  Water. — The  measurement  of  water  may  prop- 
erly be  considered  under  two  heads,  namely,  measurement  of  supply 
and  measurement  of  duty  requirement. 

Measurement  of  supply  is  for  the  purpose  of  determining  the 
quantity  of  water  available  for  irrigation,  power  development  and 
domestic  use.  It  includes  the  measurement  of  runoff  from  the  vari- 
ous streams  and  to  a  limited  degree  also  the  determination  of  under- 
ground flow  which  may  be  made  available  for  use  through  pumping 


PLATE  II 


FIG.  A. — Method  of  making  a  measurement  of  the  amount  of  water  in  a  stream, 
using  current  meter  from  bridge. 


FIG.  B. — Making  similar  measurements  by  wading. 


(Facing  Page  26) 


PLATE  II 


FIG.  C.— Meters  used  for  measuring  the  velocity  of  the  flowing  water. 


WATER  SUPPLY  27 

or  artesian  flow.  Measurement  of  duty  requirement  includes  the 
determination  of  the  amount  used  for  irrigation,  power  development 
and  other  purposes. 

Both  of  the  above  classes  of  measurements  are  necessary  in  an 
enterprise  involving  the  use  of  water;  the  first  to  determine  the 
amount  available  and  the  second  to  determine  the  extent  of  an  enter- 
prise which  a  given  supply  will  furnish. 

The  methods  of  measuring  water  in  natural  streams  in  a  systematic 
and  economical  manner  have  been  developed  within  the  last  twenty 
years,  largely  by  the  efforts  of  the  United  States  Geological  Survey. 
Notable  progress  has  been  made  in  simplifying  details  and  in  adapt- 
ing them  to  methodically  carrying  on  work  over  a  wide  extent  of 
country.  There  has  been  a  gradual  evolution  of  the  instruments 
employed,  especially  along  the  line  of  lightness  and  portability. 

Briefly  stated,  the  work  consists  of  measuring  and  recording  the 
total  quantity  of  water  which  passes  a  given  point  in  a  stream  and 
in  this  manner  determining  the  runoff  from  each  of  the  principal 
watersheds.  It  has  not  been  possible,  up  to  the  present  time,  to 
measure  all  of  the  streams  of  the  country;  enough,  however,  are 
being  measured  to  permit  rough  estimates  of  the  total  supply  being 
made  and  the  work  is  being  gradually  extended  with  the  increasing 
demand  for  water-supply  data.  Measurements  of  the  quantity  of 
water  used  in  various  enterprises  are  also  being  carried  on,  both  by 
the  United  States  and  public  utility  corporations. 

Units  of  Measurement. — Two  classes  of  units  are  commonly  used 
in  the  measurement  of  water,  the  first  representing  quantity  and  the 
second  rate  of  flow. 

Quantity  is  measured  in  terms  of  some  well-defined  unit  of  capac- 
ity and  is  used  to  express  the  amount  of  water  contained  in  a  reservoir 
or  that  applied  to  a  given  area  of  land  in  the  process  of  irrigation. 
The  units  of  quantity  commonly  used  are  the  gallon,  the  cubic  foot 
and  the  acre-foot.  The  gallon  and  cubic  foot  are  employed  in  ex- 
pressing the  quantity  of  water  stored  or  used  for  domestic  purposes, 
but,  on  account  of  the  smallness  of  each  of  these  units,  they  are  sel- 
dom used  in  engineering  estimates  of  irrigation  work.  Instead  the 
acre-foot  is  the  common  unit.  It  is  defined  as  the  amount  of  water 
required  to  cover  i  acre  i  ft.  deep  or  43,560  cu.  ft.  Capacities  of 
large  reservoirs  are  generally  given  in  acre-feet,  these  figures  being 
thus  immediately  computable  with  the  agricultural  areas. 

Rate  of  flow  may  be  defined  as  the  quantity  of  water  flowing 
through  a  pipe  or  channel  in  a  given  unit  of  time,  usually  the  second. 


28        PRINCIPLES  OF  IRRIGATION  ENGINEERING 

The  units  are  the  miner's  inch  and  second-foot.  The  miner's  inch, 
the  first  unit  expressing  rate  of  flow  generally  employed  in  the 
United  States,  is  supposed  to  represent  the  quantity  of  water  which 
flows  continuously  through  an  orifice  i  in.  square  under  a  given  head. 
The  head  on  the  orifice  has  been  variously  defined  in  different  local- 
ities but  is  ordinarily  taken  as  about  4  in.  above  the  top  of  the  orifice. 
The  second-foot  is  defined  as  i  cu.  ft.  per  second  of  time.  A  box 
or  conduit  i  ft.  square  carrying  water  with  a  velocity  of  i  ft.  per 
second  would  deliver  i  second-foot.  The  second-foot,  on  account 
of  its  definiteness,  is  the  most  desirable  unit  for  expressing  rate  of 
flow  and  the  one  commonly  used  by  American  and  English  engineers. 
By  the  latter  it  is  written  "cusec." 


FIG.  8. — Method  of  measuring  miner's  inches. 

The  miner's  inch  is  indefinite  since  the  quantity  of  water  which 
will  flow  through  an  orifice  i  in.  square  under  a  fixed  head  depends 
upon  the  thickness  of  the  medium  in  which  the  orifice  is  made.  For 
example,  the  amount  of  flow  through  an  orifice  cut  in  a  plank  2  in. 
in  thickness  will  be  very  different  from  that  through  the  same  size 
orifice  cut  in  a  thin  sheet  of  metal. 

One  of  the  methods  of  measuring  miner's  inches  is  indicated  by 
the  accompanying  illustration,  Fig.  8,  in  which  a  rectangular  orifice 
is  so  arranged  as  to  be  capable  of  adjustment  to  various  widths  by 


WATER  SUPPLY  29 

means  of  a  slide,  rendering  it  practicable  to  measure  quantities  from 
one  miner's  inch  up  to  75  inches.  This  is  fairly  satisfactory  for 
these  smaller  quantities,  but  to  measure  10,000  miner's  inches  by 
such  device  is  practically  impossible  because  of  the  fact  that  the 
orifice  must  be  of  great  horizontal  extent  to  avoid  the  complications 
of  increased  head  if  the  orifice  is  enlarged  in  a  vertical  direction. 

In  order  to  avoid  confusion  growing  out  of  the  use  of  this  unit, 
most  of  the  states  have  defined  the  miner's  inch  in  terms  of  the  second- 
foot.  In  this,  however,  there  is  not  an  agreement  among  the  various 
States.  In  Idaho,  Kansas,  Nebraska,  New  Mexico,  North  and  South 
Dakota,  50  miner's  inches  equal  i  second-foot.  In  Arizona,  Califor- 
nia, Montana  and  Oregon,  40  miner's  inches  equal  i  second-foot. 

On  account  of  its  indefiniteness  and  the  fact  that  the  miner's  inch 
is  not  well  adapted  to  expressing  the  results  of  computations  on  the 
rate  of  flow  through  flumes,  over  wiers  and  other  measuring  devices, 
the  use  of  the  term  should  be  discontinued. 

"Second-feet  per  square  mile"  is  the  average  number  of  cubic  feet 
of  water  flowing  per  second  from  each  square  mile  of  area  drained, 
on  the  assumption  that  the  runoff  is  distributed  uniformly  both  as 
regards  time  and  area. 

"Runoff  in  inches"  is  the  depth  to  which  the  drainage  area  would 
be  covered  if  all  the  water  flowing  from  it  in  a  given  period  were 
conserved  and  uniformly  distributed  on  the  surface.  It  is  used  for 
comparing  runoff  with  rainfall,  which  is  usually  expressed  in  depth  in 
inches. 

Convenient  Equivalents. — The  following  is  a  list  of  convenient 
equivalents  for  use  in  hydraulic  computations: 

i  second-foot  equals  7.48  United  States  gallons  per  second;  equals  448.8  gallons 
per  minute;  equals  646,272  gallons  for  one  day. 

second-foot  equals  6.23  British  imperial  gallons  per  second. 

second- foot  for  one  year  covers  i  square  mile  1.131  feet  or  13.572  inches  deep. 

second-foot  for  one  year  equals  31,536,000  cubic  feet. 

second-foot  equals  about  i  acre-inch  per  hour. 

second- foot  for  one  day  covers  i  square  mile  0.03719  inch  deep. 

second-foot  for  one  30-day  month  covers  i  square  mile  1.116  inches  deep. 

second-foot  for  one  day  equals  1.983  acre- feet. 

second-foot  for  one  3o-day  month  equals  59.50  acre-feet. 
100  United  States  gallons  per  minute  equals  0.223  second-foot. 
100  United  States  gallons  per  minute  for  one  day  equals  0.442  acre-foot. 
1,000,000  United  States  gallons  per  day  equals  1.55  second-feet. 
1,000,000  United  States  gallons  equals  3.07  acre-feet. 
1,000,000  cubic  feet  equals  22.95  acre-feet, 
i  acre-foot  equals  325,850  gallons. 


30        PRINCIPLES  OF  IRRIGATION  ENGINEERING 

inch  deep  on  i  square  mile  equals  2,323,200  cubic  feet. 

inch  deep  on  i  square  mile  equals  0.0737  second-foot  per  year. 

foot  equals  0.3048  meter. 

mile  equals  1.60935  kilometers. 

acre  equals  0.4047  hectare. 

acre  equals  43,560  square  feet. 

acre  equals  209  feet  square,  nearly. 

square  mile  equals  2.59  square  kilometers. 

cubic  foot  equals  0.0283  cubic  meter. 

cubic  foot  equals  7.48  gallons. 

cubic  foot  of  water  weighs  62.5  pounds. 

cubic  meter  per  minute  equals  0.5886  second-foot. 

horse-power  equals  550  foot-pounds  per  second. 

horse-power  equals  76  kilogram-meters  per  second. 

horse-power  equals  746  watts. 

horse-power  equals  i  second-foot  falling  8.80  feet. 

1/3  horse-power  equals  about  i  kilowatt. 

Sec.-ft.  X  fall  in  feet 
To  calculate  water-power  quickly:  =net  horse-power  on 

water  wheel  realizing  80  per  cent,  of  theoretical  power. 

Methods  of  Measurement. — The  measurement  of  water  is  in 
practically  all  cases  accomplished  by  taking  the  rate  and  time  of  flow 
and  computing  the  amount  of  discharge  from  these  factors.  Where 
the  rate  of  flow  is  constant  the  quantity  is  the  rate  multiplied  by  the 
time.  Where  the  rate  of  flow  varies  from  day  to  day  or,  as  is  often 
the  case,  from  hour  to  hour,  an  account  must  be  taken  of  these  varia- 
tions. This  is  done  by  computing  the  amount  of  discharge  for 
short  periods  of  time,  for  example,  a  day  or  an  hour,  and  summing  up 
these  amounts  over  the  entire  period  of  flow.  In  the  work  of  the 
United  States  Geological  Survey  the  amount  of  discharge  for  each 
day  is  used  as  a  basis  for  determining  the  mean  monthly  or  yearly 
discharge. 

The  measurement  of  rate  of  flow  or  stream  measurement  as  it  is 
usually  called  is  based  primarily  upon  measurements  of  the  cross- 
sectional  area  and  mean  velocity  through  the  measured  section.  In 
some  cases,  more  especially  on  small  streams  or  in  irrigation  or  supply 
canals,  measurements  are  made  by  special  devices,  such,  for  example, 
as  wiers. 

The  accompanying  illustration,  Fig.  9,  gives  the  ideal  arrange- 
ment of  a  fully  equipped  gaging  station.  In  the  foreground  is  a 
small  structure  enclosing  a  self-registering  device  for  keeping  record 
of  the  rise  and  fall  of  the  water  in  a  small  well  connected  with  the 
river  by  a  horizontal  pipe,  near  it  is  a  vertical  gage  rod  to  check  the 
observations  by  direct  reading.  Devices  of  this  kind  are  somewhat 


WATER  SUPPLY 


31 


expensive  to  install  and  require  frequent  skilled  attendance  to  adjust. 
In  the  background  is  a  cable  suspended  across  the  river  from  which 
is  hung  a  seat  or  small  car  from  which  the  hydrographer  can 
work  while  measuring  the  width,  depth,  and  velocity  of  various 
portions  of  the  stream.  (See  also  Plate  II,  Figs.  A  and  B,  illus- 
trating measurements  from  a  small  bridge  or  made  by  wading  the 
stream.) 

The  cross-sectional  area  of  a  stream  is  measured  by  taking  sound- 
ings at  regular  intervals,  of  say  5  or  10  ft.,  across  the  stream  and 
computing  the  areas  of  each  of  the  small  sections  between  soundings 


FIG.  9. — Equipment  for  river  station,  consisting  of  self-registering  height 
gage,  protected  by  small  house  with  cable  and  car  for  convenience  in  velocity 
measurements. 

from  its  width  and  mean  depth.  The  sum  of  the  small  areas  thus 
obtained  is  the  total  cross-sectional  area.  The  velocity  is  determined 
either  by  means  of  a  current  meter,  Plate  II,  Fig.  C,  placed  in  the 
stream,  or  by  means  of  floats  on  the  surface.  The  former  method  is 
susceptible  of  the  greater  accuracy  and  is  the  one  generally  used  in 
stream-gaging  work.  In  computing  the  discharge,  account  must  be 
taken  of  the  fact  that  the  velocity  varies  in  different  parts  of  the 
stream  and  that  it  is  necessary  to  divide  the  total  cross-section 
into  parts  and  compute  the  discharge  through  each  part  separately. 
This  can  be  done  readily  when  velocity  measurements  are  made  by 
means  of  the  current  meter  at  various  points  in  the  stream.  When 
velocity  is  measured  by  means  of  floats  it  is  generally  assumed  that 


32        PRINCIPLES  OF  IRRIGATION  ENGINEERING 

the  mean  velocity  is  about  0.8  of  the  surface  velocity.  Measure- 
ments by  this  method  are  at  best  but  rough  estimates  and  for  this 
reason  should  not  be  relied  upon  where  reasonably  accurate  results 
are  required. 

Where  conditions  will  permit  of  its  installation  and  use,  the  wier 
is  probably  the  most  accurate  method  of  measuring  water.  The 
conditions  necessary  for  accurate  wier  measurements  are  such, 
however,  that  they  frequently  cannot  be  secured  on  streams  of  any 
considerable  size.  Accurate  wier  measurements  require  first,  that 
the  water  above  the  wier  be  in  a  quiescent  state  and  that  the  fall 
be  sufficient  that  the  surface  of  the  water  in  the  stream  on  the  lower 
side  of  the  wier  be  below  the  top  of  the  wier  crest.  It  is  readily 
seen  that  these  conditions  are  difficult  to  obtain  on  streams  of  any 
considerable  size. 

Results  of  Stream  Measurement. — The  results  of  stream  measure- 
ment indicate  a  wide  fluctuation  in  the  quantity  of  flow  from  month 
to  month,  and  from  year  to  year.  As  a  rule  the  minimum  flow  is 
when  water  is  most  needed  for  irrigation  or  during  the  months  of 
July  and  August.  It  increases  gradually  as  cooler  weather  comes 
on,  continuing,  however,  at  a  relatively  small  amount  during  the 
winter,  and  reaching  the  flood  stage  during  the  spring  months. 
The  maximum  flood  follows  the  spring  rains  and  melting  snow  occur- 
ring generally  in  the  latter  part  of  May  or  in  June. 

Besides  the  annual  variations  of  drought  and  flood,  there  is  what 
is  sometimes  called  the  "non-periodic"  alternation  of  wet  and  dry 
years.  For  several  years  in  succession,  the  floods  will  be  high  and 
prolonged,  and  the  low-water  season  will  yield  a  fair  amount  of 
water  for  irrigation,  then  follows  one  or  two  or  sometimes  three 
years  in  succession  of  unusual  drought,  when  the  floods  are  very 
small  and  the  runoff  not  sufficient  to  fill  the  reservoirs  which  may 
have  been  provided.  In  planning  irrigation  works,  full  considera- 
tion must  be  given  to  the  fact  that  these  years  of  drought  frequently 
occur  in  succession. 

Attempts  have  been  made  to  discover  some  rule  governing  the 
occurrence  of  wet  and  dry  years.  One  has  worked  out  a  theory 
that  droughts  occur  at  intervals  of  seven  years,  while  another  is 
equally  certain  that  an  eleven-year  period  is  more  nearly  correct, 
and  still  again  there  are  advocates  of  a  seventeen-year  period.  For 
practical  purposes,  there  is  no  rule  which  can  be  depended  upon 
other  than  that  whatever  has  happened  in  the  way  of  extreme 
drought  or  flood  is  likely  to  happen  again,  and  that  a  series  of  wet 


WATER  SUPPLY  33 

years  is  likely  to  be  followed  by  dry  years,  the  length  of  duration  of 
each  of  these  periods  being  unknown. 

The  actual  quantities  of  water  in  the  principal  streams  month 
by  month  and  year  by  year  is  given  in  the  publications  of  the  United 
States  Geological  Survey,  these  quantities  being  stated  both  in 
average  rate  of  flow  or  cubic  feet  per  second,  and  in  total  quantity 
delivered  during  the  period  in  acre-feet. 

Quality  of  Water  Supply. — In  addition  to  its  quantity,  the  quality 
of  a  water  supply  to  be  used  for  irrigation  should  be  examined. 
Water  in  its  flow  dissolves  and  carries  out  of  the  soil  or  rock  over 
which  it  travels  small  quantities  of  mineral  or  alkali  salts.  As  a 
result  of  this  gradual  accumulation,  no  stream  waters  are  absolutely 
pure.  Some  of  these  salts  are  harmless,  while  others  are  highly 
injurious  to  plant  growth. 

In  the  arid  west  where  the  rainfall  is  limited,  and  where,  as  is 
frequently  the  case,  the  character  of  the  rock  is  such  that  disintegra- 
tion proceeds  rapidly,  the  quantity  of  salts  in  solution  is  far  greater 
than  in  the  more  humid  regions  of  the  east.  Where  the  rocks  are 
mostly  crystalline,  such  as  the  granites,  the  stream  waters  are  more 
nearly  free  from  matter  in  solution,  but  where  the  flow  is  over  shales, 
they  frequently  become  highly  charged.  If  waters  used  for  irriga- 
tion contain  any  considerable  quantity  of  salts  in  solution,  there  is 
danger  of  the  soil  becoming  sufficiently  impregnated  to  render  it 
unfit  for  growing  crops.  This  is  especially  the  case  if  the  soils 
themselves  previous  to  irrigation  contain  a  small  amount  of  these 
harmful  soluble  salts. 

There  is  no  hard  and  fast  rule  as  to  the  amount  of  soluble  salts 
or  alkali  required  to  render  water  unsafe  for  irrigation  purposes. 
This  will  depend  upon  the  character  of  the  salts,  the  natural  con- 
ditions of  the  soil,  the  amount  of  water  used  in  irrigation  and  the 
efficiency  of  underground  drainage  to  prevent  alkali  accumulation 
on  the  surface.  Few  of  the  natural  stream  waters  are  unfit  for  irri- 
gation purposes  if  proper  precautions  are  taken  in  their  use,  and  the 
lands  to  which  they  are  applied  are  not  already  strongly  charged 
with  alkali.  It  is  important  to  know  the  quality  of  waters,  not  for 
the  purpose  of  condemning  them  but  to  insure  their  proper  use. 

It  is  frequently  stated  that  one-tenth  of  i  per  cent,  of  soluble 
salts,  or  100  parts  of  salts  in  100,000  of  water,  is  the  limit  of  safety 
in  irrigation  waters.  There  are,  however,  instances  where  water 
containing  two  or  three  times  this  amount  have  been  used  without 
notable  injury.  On  the  other  hand,  waters  containing  less  than  half 

3 


34        PRINCIPLES  OF  IRRIGATION  ENGINEERING 

this  amount  when  carelessly  used  have  been  known  to  injure  large 
areas.  In  passing  upon  the  quality  of  irrigation  waters  the  character 
of  the  soluble  salts  they  contain  and  the  conditions  under  which  they 
are  to  be  used  must  be  considered. 

Amount  of  Water  Required  for  Irrigation. — The  amount  of  water 
which  is  required  for  successful  production  of  crops  is  dependent 
upon  the  climate,  soil,  and  kind  and  number  of  crops  grown.  As 
a  rule,  where  water  is  plentiful,  too  much  is  applied  to  the  land, 
especially  by  unskilled  irrigators.  The  most  skillful  irrigator  ob- 
tains the  best  results  with  the  smallest  amount  of  water.  Thorough 
cultivation  rather  than  excess  use  of  water  is  the  secret  of  success 
and  the  man  who  attempts  to  save  labor  in  cultivating  by  putting 
on  additional  water  will  usually  reduce  the  crop  production  and  en- 
danger his  own  and  possibly  also  his  neighbor's  land. 

Roughly  stated,  the  amount  of  water  required  for  successful 
irrigation  varies  from  i  to  3  acre-feet  per  acre  per  annum,  or  an 
amount  sufficient  to  cover  the  land  from  i  to  3  ft.  in  depth.  In 
some  sections  of  extreme  aridity,  where  climatic  conditions  are  such 
that  crops  grow  during  practically  the  entire  year,  this  latter 
amount  may  be  exceeded. 

Heavy  soils  through  which  water  percolates  but  slowly  require, 
as  a  rule,  less  water  than  the  more  porous  soils.  These  soils,  how- 
ever, require  thorough  cultivation  to  keep  them  in  proper  condition 
to  absorb  and  hold  the  water  which  is  applied  to  them.  Under 
drought  conditions,  excellent  crops  have  been  raised  and  orchards 
caused  to  produce  heavily  with  water  carefully  applied  at  the  rate 
of  only  i  or  i  1/2  acre-feet  per  acre  per  annum. 


CHAPTER  IV 
DESIGN  AND  CONSTRUCTION  OF  CANALS 

Capacity. — The  capacity  of  a  canal  at  any  given  point  is  the 
amount  of  water  which  will  pass  that  point  under  normal  conditions. 
In  preparing  plans  for  construction  or  enlargement  it  is  necessary  to 
know  the  agricultural  area  which  the  canal  is  to  serve  and  the  duty 
of  water  for  which  provisions  must  be  made  during  the  period  of 
greatest  irrigation  requirement.  In  considering  the  total  annual  de- 
mand for  water  it  is  advisable  to  divide  the  requirements  into  months 
or  shorter  periods  covering  the  entire  irrigation  season.  Where  data 
are  not  at  hand  to  determine  the  actual  amount  of  water  required 
for  maximum  irrigation  during  any  one  month,  various  assumptions 
must  be  made  and  these  estimates  should  be  sufficiently  liberal  to 
provide  for  all  future  emergencies.  If,  for  example,  it  is  known  that 
during  an  irrigation  season  of  say  six  months  in  length,  30  in. 
in  depth  or  2  1/2  acre-feet  per  acre  is  required,  it  is  probably  safe 
to  assume  at  least  40  per  cent,  in  excess  of  this  average  amount, 
or  a  depth  of  7  1/2  inches,  may  be  required  in  a  single  month  during 
the  period  of  greatest  irrigation. 

Having  arrived  at  the  amount  of  water  needed  in  the  month  of 
maximum  demand  the  capacity  of  canal  is  found  by  multiplying  the 
depth  in  feet  of  water  required  by  the  total  number  of  acres  to  be 
supplied  and  dividing  by  the  number  of  days  in  the  month.  This 
will  give  the  number  of  acre-feet  required  daily,  which  may  be  re- 
duced to  second-feet  by  again  dividing  by  1.98,  since  i  second- 
foot  continuous  flow  for  twenty-four  hours  equals  1.98  acre-feet. 

The  above  is  satisfactory  for  the  design  of  main  canals  or  large 
laterals  where  a  practically  continuous  flow  can  be  maintained 
from  "day  to  day.  In  the  design  of  smaller  canals  or  laterals,  in- 
tended to  serve  but  a  small  area,  account  must  be  taken  of  the  fact 
that  such  canals  may  not  be  in  continuous  use.  Provision  must 
be  made  for  delivering  the  required  amount  of  water  during  the 
period  of  time  that  irrigation  will  probably  be  carried  on  from  such 
canal.  For  example,  a  canal  with  a  carrying  capacity  of  10  cu.  ft. 
per  second  will  deliver  approximately  20  acre-feet  per  day,  or  6co 
acre-feet  per  month.  Such  a  canal  with  a  maximum  duty  of  water 

35 


36        PRINCIPLES  OF  IRRIGATION  ENGINEERING 

of  1/2  acre-foot  per  month  is  capable,  theoretically,  of  irrigating 
1,200  acres.  It  is  probable,  however,  that  the  irrigation  of  a  tract 
of  this  size  for  economic  results  will  not  require  continuous  irrigation, 
but  that  irrigation  may  be  carried  over  the  entire  area  in  a  period 
of  from  ten  to  fifteen  days  and  no  further  application  of  water  might 
be  required  for  an  equal  period  of  time. 

In  fixing  the  capacity  of  a  canal  it  is  necessary  to  take  account  of 
the  actual  time  that  the  canal  is  to  be  in  operation  and  to  provide 
for  delivering  the  amount  of  water  required  during  this  period. 
Account  must  also  be  taken  of  probable  losses  by  seepage  and 
evaporation.  The  amount  of  these  will  depend  upon  the  length 
of  the  canal,  the  nature  of  material,  and  climatic  conditions.  No 
definite  rules  can  be  laid  down  for  their  determination.  Where 
data  are  at  hand  relative  to  seepage  and  evaporation  losses  -these 
can  be  determined.  Where  such  data  are  not  at  hand,  estimates 
for  them  must  be  made.  The  capacity  of  a  canal  should  be  suf- 
ficient to  provide  for  the  net  quantity  of  water  required  on  the 
land  in  addition  to  the  evaporation  and  seepage  losses  which  are 
expected. 

A  convenient  method  of  determining  the  capacity  of  a  canal 
required  for  a  given  area  is  to  first  find  the  area  which  will  be  served 
by  a  continuous  flow  of  i  cu.  ft.  of  water  per  second,  which  may 
be  computed  as  follows: 

Let  a  =  area 

d  =  maximum  duty  of  water,  that  is,  the  depth  required  on  the 

land  for  a  given  period  of  time 
/  =  number  of  days  in  the  period  considered 
p  =  percentage  of  loss  by  seepage  and  evaporation  from  the 

canal 
Then 

43,560  ad  =  86,400  t(i.oo-p) 
or 

_86,40o/(i.oo-p)_i.98  t(i.oo-p) 
43,560  d         d 

If  we  assume  the  duty  of  water  for  a  period  of  thirty  days  to  be 
0.6  ft.  on  the  land  and  the  loss  by  seepage  and  evaporation  in  the 
canal  to  be  10  per  cent,  of  the  total  flow, 

1.98X30X0.90 
a=  =79-i  acres 

Location  of  Canals. — Under  the  term  " location"  of  a  canal  is 


DESIGN  AND  CONSTRUCTION  OF  CANALS          37 

included  its  relation  to  the  source  of  supply,  the  points  of  delivery 
and  all  other  natural  or  cultural  conditions.  In  locating  canals 
there  are  to  be  considered,  among  other  items,  (a)  economy  of  con- 
struction and  maintenance;  (b)  safety  against  possible  breaks;  (c) 
the  maximum  amount  of  land  that  can  be  irrigated  under  the  system. 
Preliminary  surveys,  sufficient  to  determine  a  close  approximation  to 
the  area  to  be  watered  must  first  be  made.  With  this  data  and  an 
assumed  duty  of  water,  the  capacity  of  the  canal  can  be  determined. 
The  next  step  is  to  design  a  typical  section  of  canal  and  fix  its  slope. 
The  various  questions  to  be  considered  in  this  design  are  treated  in  a 
later  paragraph,  so  that  for  the  present  it  is  sufficient  to  assume  as 
fixed  the  cross-section  of  the  canal  and  banks  and  the  grade  upon 
which  the  location  is  to  be  made. 

For  economic  construction  a  canal  should  be  so  located  that  the 
excavations  will  equal  the  embankments,  with  a  reasonable  allow- 
ance, say  about  10  per  cent,  for  shrinkage.  The  depth  of  cut  neces- 
sary for  this  is  defined  as  the  normal  or  economic  cut.  Before 
starting  the  actual  work  of  location  in  the  field  the  economic  cut  for 
level  ground  and  side  slopes  of  various  degrees  should  be  computed, 
for  the  ready  reference  of  the  engineer  in  charge  of  the  location. 
Data  of  this  kind  are  valuable  for  use  in  the  field  in  determining  the 
location  for  minimum  cutting,  which  is  one  of  the  important  factors 
in  location. 

Besides  the  minimum  amount  of  excavation  it  is  necessary  to 
consider  other  factors.  On  sloping  ground  it  is  often  necessary 
to  excavate  more  material  than  is  required  for  banks  in  order  to  put 
the  waterway  sufficiently  in  cut  to  insure  safety.  In  locating  along 
a  slope  broken  by  long  narrow  ridges  it  is  frequently  a  matter  of  econ- 
omy and  good  engineering  on  account  of  savings  in  length  and  in  the 
elevation  of  water  surface,  to  cut  through  the  ridges  rather  than 
attempt  to  go  around  them  on  approximately  the  contour  of  the  canal. 
The  same  remarks  apply  equally  to  the  crossing  of  long  and  narrow 
depressions  or  draws,  where  the  amount  of  material  excavated  is  not 
sufficient  and  material  has  to  be  hauled  from  the  adjacent  ridges  or 
taken  from  borrow  pits  to  form  the  banks.  It  is  frequently  advisable 
to  locate  two  or  more  alternate  lines  and  make  preliminary  estimates 
of  cost  before  the  final  location  is  determined. 

Where  fills  are  contemplated  careful  attention  should  be  given  the 
location  on  account  of  the  great  danger  of  breaks  and  of  increased 
cost  of  maintenance.  In  locating  the  larger  main  canals  especially, 
the  question  of  safety  should  be  given  first  consideration.  It  must  be 


38        PRINCIPLES  OF  IRRIGATION  ENGINEERING 

remembered  that  the  extra  cost  of  maintenance  of  a  canal  on  a 
treacherous  location,  while  an  important  factor,  is  of  less  importance 
than  the  possible  losses  of  crops  by  the  failure  of  the  canal  during 
that  period  of  an  irrigation  season  when  water  is  most  needed.  This 
is  notably  true  in  extreme  arid  regions  where  the  application  of  water 
is  an  absolute  necessity  for  agricultural  operations. 

Alignment. — The  accurate  alignment  of  a  canal  is  of  secondary 
importance  to  economic  and  safe  location.  The  elimination  of 
sharp  turns  and  reduction  of  curvature  is  desirable  in  order  to  reduce 
the  length  and  to  guard  against  erosion,  which  sometimes  occurs  on 
short  curves.  The  requirements  of  alignment  presented  in  the  loca- 
tion of  a  canal  are  less  rigid  than  in  railroad  work.  There  are,  how- 
ever, certain  matters  which  should  be  given  consideration.  At  the 
end  of  long  tangents,  where  wave  action  may  prove  considerable,  as  is 
the  case  in  large  canals,  the  curves  should  be  made  as  gentle  as 
possible  in  order  to  avoid  washing  of  banks.  Especial  precautions 
should  be  taken  if  the  exposed  bank  is  in  fill.  Shorter  curves  may 
be  used  with  the  same  degree  of  safety  if  the  curve  is  thrown  into  the 
slope,  as  is  the  case  when  passing  around  the  head  of  a  draw,  than 
when  the  curve  is  thrown  outward  as  in  passing  around  the  point  of  a 
ridge.  This  is  on  account  of  the  greater  velocity  and  increased 
tendency  to  erosion  on  the  outside  of  the  curves. 

The  precise  amount  of  resistance  which  a  curve  offers  to  the  flow 
of  water  in  open  channels  has  not  been  definitely  determined.  It  is 
believed,  however,  for  velocities  of  flow  which  are  safe  for  earthen 
canals  that  a  curve  in  the  center  line  whose  radius  is  two  and  one- 
half  times  the  bottom  width  of  the  canal  may  be  used  without  any 
appreciable  effect  on  the  average  rate  of  flow.  The  above  rule  is 
considered  by  some  engineers  as  a  safe  one  to  apply  in  determining 
the  alignment  of  canals.  There  are,  however,  numerous  examples 
where  this  curvature  is  exceeded  and  satisfactory  results  obtained, 
especially  where  a  canal  is  principally  in  cut,  so  that  erosion  does  not 
have  the  effect  of  weakening  the  banks. 

Cross-section. — The  selection  of  a  cross-section  for  a  canal  is  one 
involving  economy  of  construction  and  maintenance  as  well  as  se- 
curity against  failures  which  may  prove  disastrous  to  an  irrigation 
system.  It  requires  the  consideration  of  the  theory  of  flow  of  water 
in  channels  and  the  exercise  of  engineering  judgment.  From  the 
standpoint  of  theory  alone  it  would  appear  the  section  which  will  (a) 
carry  the  necessary  amount  of  water;  (b)  conserve  grade  so  as  to 
cover  the  greatest  possible  area  and,  (c)  require  the  least  amount 


DESIGN  AND  CONSTRUCTION  OF  CANALS          39 

of  excavation  in  its  construction,  is  the  one  which  should  be  selected. 
For  a  canal  of  given  slope  and  fixed  area  of  cross-section  the  greatest 
velocity  will  be  attained  by  selecting  the  section  with  the  maximum 
hydraulic  radius.  From  this  it  follows  that  such  a  section  will  re- 
quire less  grade  for  the  same  capacity  than  any  other  of  equal  area. 
It  can  be  shown  that  a  circular  or  semi-circular  section  has  the  largest 
hydraulic  radius  for  a  given  area.  It  can  also  be  shown  for  rectangular 
and  trapezoidal  sections  that  when  the  width  of  surface  is  equal  to 
the  sum  of  the  two  side  slopes  and  the  hydraulic  radius  is  equal  to 
one-half  of  the  depth  of  water  the  hydraulic  radius  is  a  maximum. 
The  most  advantageous  rectangular  section  is  one  whose  top  width 
is  equal  to  twice  the  depth.  For  trapezoidal  sections  certain  fixed 
relations  between  width  and  depth  of  water,  depending  upon  the 
steepness  of  side  slopes,  must  be  maintained  in  order  to  get  a  maxi- 
mum hydraulic  radius.  These  relations,  for  a  few  of  the  more  com- 
mon slopes  in  use,  are  as  follows: 

Slopes  1/2  hor.  to  i  ver. — surface  width  =2. 24 X depth. 
Slopes  i  hor.  to  i  ver. — surface  width  =2. 83  X depth. 
Slopes  1 1/2  hor.  to  i  ver. — surface  width  =  3. 60 X depth. 
Slopes  2  hor.  to  i  ver. — surface  width  =  4.47  X depth. 

These  sections,  while  theoretically  the  most  advantageous, 
are  generally  not  the  most  practical,  on  account  of  the  excessive 
depths  required  for  canals  of  large  cross-sectional  areas.  Th6 
accompanying  illustration  indicates  sections  on  which  canals  have 
been  built  under  ordinary  conditions  of  nearly  level  or  slightly 
sloping  ground. 

In  building  earthen  canals  it  is  necessary,  for  the  sake  of  economy, 
to  utilize  the  embankments  to  form  a  part  of  the  waterway.  In 
other  words,  the  water  must  be  held  in  part  against  the  made  em- 
bankments. In  order  to  reduce  seepage  and  minimize  the  danger  of 
breaks  it  is  advisable  also  to  limit  the  pressure  or  head  against  artificial 
banks.  Generally  a  wide  and  shallow  canal  is  less  liable  to  cause 
trouble  due  to  seepage  than  a  narrow  and  deep  one.  The  shallow 
canal,  on  the  other  hand,  for  the  same  area  of  cross-section,  requires 
more  grade  to  give  it  the  same  carrying  capacity  than  a  narrow 
and  deep  canal.  The  relative  advantages  of  various  types  of 
section  has  been  the  subject  of  considerable  discussion  among 
irrigation  engineers.  The  arguments  presented,  while  of  value 
in  considering  an  individual  case,  do  not  lead  to  general  conclusions. 
The  narrow  and  deep  section,  while  generally  requiring  a  less  amount 


40        PRINCIPLES  OF  IRRIGATION  ENGINEERING 

of  excavation  for  a  given  capacity  and  grade,  may  prove  the  more 
expensive  of  construction  on  account  of  the  character  of  excavation 
encountered,  and  difficulty  of  removing  materials  from  a  greater 
depth.  A  wide  and  shallow  canal  on  side  hills  has  the  disadvantage 
of  requiring  large  amounts  of  excavation  on  the  upper  side,  and 
does  not  permit  of  keeping  the  waterway  well  within  the  excavated 
portion  of  the  channel  on  the  lower  side  without  considerable  cost. 
No  fixed  rules  for  the  selection  of  a  canal  section  can  be  formu- 
lated, but  each  particular  case  must  be  treated  with  due  regard 


^  :  -~  --.-•-- — 


On  Level  or  nearly  Level  Ground 


_  _J-«Ll-"'"^5-  -^     ~  ~—~  -*-=— -~- 

•» 


In  through  Cut 
Original  Surface 


30 H 

Typical  Canal  Sections 


FIG.  10. — Typical  cross-section  of  irrigation  canals  in  level  or  sloping  ground 
and  in  relatively  firm  material. 

to  safety  and  economy  of  construction.  In  practice  it  is  necessary 
to  consider  the  maximum  depth  of  water  a  canal  can  safely  carry, 
the  height  of  water  surface  above  the  natural  ground  surface,  and 
the  depth  to  which  excavations  can  be  made  economically.  In 
large  canals  these  factors  will  ordinarily  control  in  fixing  the  depth 
of  section  and  the  area  required  for  necessary  capacity  will  determine 
the  width.  For  small  canals,  where  the  depth  is  not  great  and  where 
grade  is  sometimes  an  important  factor,  consideration  should  be 
given  to  the  section  of  greatest  hydraulic  radius. 

Canals  on  comparatively  level  ground  are  sometimes  constructed 


DESIGN  AND  CONSTRUCTION  OF  CANALS          41 

by  placing  the  embankment  back  a  few  feet  from  the  upper  slope 
of  the  excavation,  thus  forming  a  berm.  The  effect  of  this  is  to 
increase  the  cross-sectional  area  without  increasing  the  amount 
of  excavation.  On  account  of  the  comparatively  shallow  water  near 
the  embankments,  the  velocities  in  this  portion  of  the  section  are 
reduced  and  there  is  less  tendency  to  erosion  of  the  banks.  The 
section  of  a  canal  constructed  with  a  berm,  except  over  very  flat 
country,  is  irregular  in  area,  the  water  being  restricted  to  a  narrow 
channel  where  cuts  are  deep  and  allowed  to  widen  out  where  the 
cutting  is  shallow.  Where  it  is  necessary  to  operate  canals  at 
varying  capacities  the  berms  are  alternately  wet  and  dry,  and 
conditions  are  favorable  for  a  growth  of  weeds  and  grass.  It  is 
believed  that  in  general,  berms  are  a  disadvantage  rather  than  an 
advantage  and  that  the  most  satisfactory  results  are  attained  by  the 
use  of  a  uniform  cross-section  with  side  slopes  sufficiently  flat  to 
prevent  erosion  and  a  gradual  sloughing  into  the  canal. 

Slopes  and  Width  of  Banks. — The  degree  of  steepness  of  the 
slopes  to  which  canal  banks  should  be  constructed  depends  largely 
upon  the  character  of  materials.  As  has  been  shown  in  the  previous 
paragraph,  the  steeper  the  inner  side  of  the  banks,  the  less  the 
amount  of  excavation  required  in  order  to  form  a  channel  of  given 
capacity.  This  is  more  marked  in  deep  cuts,  where  a  large  part  of 
the  excavation  is  above  the  water  section.  It  follows,  then  for 
deep  cuts  that  the  slopes  of  banks  should  be  made  as  steep  as  the 
material  will  stand  with  safety.  This  varies  from  about  1/2  hori- 
zontal to  i  vertical  for  rock  to  about  3  horizontal  to  i  vertical  for 
ordinary  light  earth.  In  some  cases  slopes  may  be  made  steeper 
than  1/2  to  i;  in  general,  however,  slopes  steeper  than  this  ex- 
cept in  very  firm  rock  have  a  tendency  to  slough,  due  to  weather- 
ing, which  results  in  a  gradual  filling  of  the  channel. 

For  earthen  slopes,  material  is  seldom  encountered  that  will 
stand  on  a  greater  slope  than  i  1/2  to  i.  In  that  portion  of  the 
channel  forming  the  waterway,  there  is  a  tendency  for  the  sides 
to  be  gradually  eroded  or  eaten  away  by  the  action  of  the  water. 
The  greatest  erosion  usually  takes  place  a  short  distance  below  the 
surface  of  the  water  and  from  this  point  the  cutting  gradually 
decreases  toward  the  bottom.  The  effect  of  this  erosion  is  to  form 
a  rounded  channel  in  which  the  sharp  angle  of  intersection  between 
sides  and  bottom  is  eliminated.  The  general  result  is  a  flattening 
of  the  sides  of  the  entire  bank,  due  to  erosion  and  the  weathering 
cf  the  material  above  where  the  erosion  takes  place.  Banks  con- 


42        PRINCIPLES  OF  IRRIGATION  ENGINEERING 


.S 


DESIGN  AND  CONSTRUCTION  OF  CANALS         43 

structed  with  i  1/2  to  i  slopes  after  a  few  years  are  found  to  have 
become  2  to  i  or  even  flatter.  When  it  is  desired  to  maintain  a 
roadway  on  the  top  of  an  embankment  it  is  necessary  to  construct 
it  somewhat  wider  than  will  be  eventually  required  on  account 
of  the  reduction  in  width  which  follows  the  flattening  of  the  slopes. 
Where  the  embankments  are  constructed  with  flat  slopes  the  tend- 
ency for  the  top  width  to  decrease  is  lessened.  On  the  outer  slopes 
of  banks  there  is  a  less  tendency  to  flattening,  partly  due  to  absence 
of  water  against  them  and  the  consequent  effects  of  erosion  and 
softening  of  the  material.  In  very  light  materials,  however,  wind 
action  may  have  an  important  effect  in  reducing  the  outer  slope. 
One  of  the  dangers  in  too  steep  outer  slopes,  especially  in  new  canals, 
is  the  tendency  to  slough  or  run  when  the  bank  becomes  saturated. 
This  danger  may  become  serious  in  banks  of  considerable  height 
built  of  light  permeable  material.  The  top  width  of  banks  required 
and  their  height  above  the  water  surface  in  the  canal  are  questions 
to  be  decided  in  each  particular  case  and  will  depend  upon  the 
depth  of  water  and  character  of  the  materials  of  which  the  banks 
are  constructed.  For  the  larger  and  more  important  canals  it 
is  believed  that  the  height  of  banks  above  the  maximum  water 
surface  should  not  be  less  than  3  ft.  and  the  top  width  not  less  than 
8  or  10  ft.  Where  a  roadway  is  maintained  on  the  top  of  banks 
this  width  should  be  increased. 

Material  for  Banks. — Ordinarily  there  is  but  little  choice  of  mate- 
rials for  forming  the  waterway  for  canals,  since  in  most  cases  it  is 
necessary,  to  keep  the  cost  within  reasonable  limits,  to  use  for  this 
purpose  the  natural  materials  found  on  the  canal  location.  It 
frequently  occurs  that  canals  are  required  to  be  constructed  through 
soils  or  rocks  which  are  exceedingly  pervious  to  water,  and  the  en- 
gineer is  called  upon  to  decide  whether  or  not  a  channel  can  be 
constructed  that  will  be  reasonably  water  tight.  This  question 
involves  not  only  that  part  of  the  waterway  formed  above  the 
natural  ground  surface  by  means  of  artificial  banks  but  applies  to 
that  portion  of  the  channel  which  is  in  cut  also  especially  on  side- 
hill  work.  Clay  is  perhaps  the  least  permeable  of  the  various  mate- 
rials through  which  canals  are  built,  while  coarse  sand  or  gravel 
offer  least  resistance  to  the  passage  of  water.  The  question  of 
permeability  of  earth  depends  upon  the  amount  of  fine  material 
which  it  contains.  Sand  or  gravels  are  composed  of  solid  particles 
of  appreciable  dimensions,  voids  of  notable  size  occurring  between  the 
particles.  The  same  is  also  true  in  broken  or  shattered  rock  forma- 


44        PRINCIPLES  OF  IRRIGATION  ENGINEERING 

tion,  where  the  spaces  between  the  rock  are  not  filled  with  earth  or 
other  fine  material.  Clay,  on  the  other  hand,  composed  of  fine 
particles,  has  correspondingly  small  voids,  so  small  as  not  to  permit 
the  ready  passage  of  water. 

In  addition  to  the  question  of  permeability,  the  character  of  the 
materials  should  be  taken  into  account  in  fixing  the  cross-section, 
the  slopes  of  banks  and  the  velocities  which  can  safely  be  maintained. 
Where  the  quantity  of  material  capable  of  making  a  water-tight  bank 
is  limited,  a  segregation  of  materials  is  sometimes  necessary,  the 
water-tight  material  being  placed  either  on  the  inner  face  or  in  the 
form  of  a  core  in  the  center  of  the  bank.  In  general  it  is  more 
economic  to  place  this  material  on  the  inner  slope  of  the  canal  than 
in  the  center  of  the  bank.  In  this  position,  however,  there  is  some 
danger  of  the  face  of  the  slopes  being  carried  away  by  erosion,  or 
by  a  breaking  down  into  the  canal,  thus  leaving  the  porous  sub- 
strata exposed. 

The  treatment  of  side  slopes  applies  equally  well  to  the  bottom  of 
canals  in  porous  materials.  Soils  and  loams  which  contain  a  con- 
siderable amount  of  vegetable  matter  usually  form  tight  banks,  but, 
on  account  of  the  material  being  comparatively  light,  require 
relatively  flat  slopes.  Sufficient  clay  mixed  with  sand  or  gravel  to 
fill  up  the  pores  and  give  it  solidity  makes  a  good  material  for  banks. 
In  constructing  canals  where  different  materials  are  encountered  in 
the  excavations,  it  is  good  practice  to  specify  that  the  coarse  mate- 
rials shall  be  placed  in  the  outer  and  the  finer  materials  in  the  inner 
portion  of  the  banks. 

Grades  and  Velocities. — The  grades  of  canals  are  fixed  in  many 
cases  by  practical  rather  than  by  theoretical  considerations.  Where 
the  grade  must  be  kept  to  the  minimum  in  order  to  reach  the  largest 
practicable  area  of  irrigable  land  the  relative  elevations  of  the  head  of 
a  canal  and  the  lands  are  the  controlling  factors.  In  this  case, 
velocity  and  some  economy  of  construction  of  the  canal  is  sacrificed 
in  order  to  increase  the  irrigable  area.  The  problem  which  the 
engineer  is  required  to  solve  is  to  find  the  point  of  balance  between  the 
extra  cost  of  construction  and  the  value  of  the  additional  lands 
which  may  be  irrigated.  Where  there  is  ample  grade,  so  that  the 
holding  up  of  a  canal  is  unnecessary,  the  problem  presented  is  one 
of  greatest  economy  of  design  and  construction  consistent  with 
safety  and  economy  of  operation. 

There  are  certain  limitations  which  cannot  be  overlooked.  If 
the  grade  of  a  canal  is  too  flat  and  the  corresponding  velocity  of 


DESIGN  AND  CONSTRUCTION  OF  CANALS          45 

flow  too  low  there  is  a  constant  tendency  to  a  filling  up  of  the  canal 
due  to  deposits  of  silt  from  waters  carrying  material  in  suspension. 
The  growth  of  noxious  weeds  and  grasses  in  a  canal  is  also  facilitated 
by  reducing  the  velocity  beyond  certain  limits.  Where  grades  are 
too  steep  and  velocities  correspondingly  high,  erosion  of  the  channel 
is  the  result. 

The  ideal  grade  for  a  canal  is  one  which  will  neither  cause  erosion 
nor  permit  silt  to  be  deposited.  This  condition,  however,  cannot 
be  fully  realized,  on  account  of  the  different  materials  through 
which  canals  must  be  constructed  and  the  varying  character  of  the 
materials  carried  in  suspension.  In  order  to  prevent  erosion  in 
canals  it  has  been  considered  necessary  that  the  velocities  be  kept 
below  certain  limits  for  different  classes  of  materials.  These 
limits  are  ordinarily  stated  to  be  from  about  21/2  ft.  per  second  for 
very  light  soils  to  from  5  to  7  ft.  per  second  for  the  firmest  earth 
materials.  It  is  generally  considered  that  erosion  is  a  function  of 
the  velocity  and  that  account  need  not  be  taken  of  the  grades 
necessary  to  produce  this  velocity  in  canals  of  different  sizes  and 
shapes  of  section.  A  further  consideration  of  the  subject  seems  to 
show  that  erosion  in  a  canal  is  a  function  of  the  grade,  size  and 
shape  of  the  section,  as  well  as  the  velocity,  or,  in  other  words,  it 
is  dependent,  to  a  certain  extent,  upon  the  amount  of  energy  ex- 
pended by  the  current  in  overcoming  the  resistance  of  friction  in  the 
channel. 

This  point  may  be  illustrated  by  considering  two  canals  of  similar 
cross-sections,  but  of  such  relative  sizes  that  the  smaller  requires 
twice  the  grade  of  the  larger  to  produce  the  same  velocity  of  flow. 
It  is  evident  that  the  energy  expended  per  unit  quantity  of  water  in 
overcoming  friction  will  be  larger  and  consequently  the  tendency  to 
erosion  greater  in  the  smaller  or  canal  of  steeper  grade.  The  same 
principle  applies  to  canals  of  equal  cross-sectional  areas  but  of  such 
different  shapes  of  cross-sections  that  more  grade  is  required  in  one 
than  the  other  to  maintain  the  same  velocity.  The  question  as  to 
how  much  erosion  in  canals  is  affected  by  increased  grades,  velocities 
remaining  constant,  is  one  upon  which  experimental  data  are  lack- 
ing. Observations  on  large  and  small  canals  constructed  in  the 
same  character  of  materials  seem  to  indicate  that  the  small  canals 
erode  under  lower  velocities  than  larger  canals.  Take,  for  example, 
a  canal  4  ft.  wide  on  the  bottom  with  11/2  to  i  side  slopes  and 
carrying  water  3  ft.  deep.  The  hydraulic  mean  radius  for  this 
caual  is  approximately  1.7;  with  a  grade  of  0.00125,  or  6.6  ft.  per 


46        PRINCIPLES  OF  IRRIGATION  ENGINEERING 

mile  and  a  value  of  ^  =  0.025  the  velocity  of  flow  is  approximately 
2.90  ft.  per  second.  Erosion  under  these  conditions  would  probably 
take  place,  except  in  the  firmest  materials.  A  canal  40  ft.  wide  on 
the  bbttom  with  i  1/2  to  i  side  slopes  and  carrying  water  10  ft. 
deep  would  have  a  hydraulic  mean  radius  of  7.6  and  with  n  =  0.025 
would  require  a  grade  of  0.00015,  or  °-8  ft.  per  mile  to  give  it  the 
same  mean  velocity.  The  latter  grades  and  velocity  would  not  be 
considered  excessive,  and  erosion  would  probably  not  occur  in 
average  firm  soil. 

Silting  of  channels  is  a  subject  to  which  comparatively  little  atten- 
tion has  been  given  in  the  United  States  on  account  of  the  relatively 
small  amount  of  silt  usually  carried  by  irrigation  canals.  In  India 
and  Egypt,  where  large  quantities  of  silt  are  taken  into  canals, 
considerable  attention  has  been  given  to  velocities  and  forms  of 
cross-sections  to  prevent  deposit  of  this  material.  The  velocity 
required  to  prevent  such  deposit  is  dependent  upon  the  character 
and  fineness  of  the  material  carried.  It  has  been  the  common  theory 
that  a  velocity  of  2  ft.  per  second  was  sufficient  to  prevent  the  deposit 
of  silt.  It  is  probable,  however,  that  a  careful  series  of  observations 
under  different  conditions  would  show  that  in  some  cases  silt  would 
be  carried  by  lower  and  in  other  cases  deposited  by  higher 
velocities. 

Mr.  R.  G.  Kennedy,  who  has  made  extended  studies  and  observa- 
tions on  silting  of  canals  in  India,  advances  the  theory  that  the  silt- 
carrying  power  of  a  canal  is  a  function  of  the  depth  of  water  as  well 
as  of  the  velocity.  From  his  experiments  Mr.  Kennedy  has  worked 
out  an  empirical  formula  showing  the  relation  between  limiting 
velocity  at  which  silt  will  be  deposited  and  depth  of  water,  as  follows : 
V  =  Cdm  in  which  V  =  velocity  at  which  silt  begins  to  deposit,  d  the 
depth  of  water  and  c  and  m  constants.  The  values  of  these  con- 
stants as  determined  are  ^  =  0.84  and  ^=0.64.  This  theory  shows 
that  silt  will  be  carried  by  a  less  velocity  in  shallow  than  in  deep 
canals. 

It  has  been  found  in  practice  that  the  varying  of  the  cross-section 
and  grade  of  a  canal  each  have  a  tendency  to  produce  erosion  and 
silt  deposits,  and  that  the  best  results  are  obtained  by  maintaining 
a  uniform  section  and  slope. 

The  following  is  a  table  of  hydraulic  functions  of  some  of  the 
principal  canals  constructed  by  the  U.  S.  Reclamation  Service. 
The  values  given  for  "n"  are  those  assumed  in  the  design  of  the 
canals. 


DESIGN  AND  CONSTRUCTION  OF  CANALS 


47 


SECTIONS  AND  SLOPES  OF  SOME  OF  THE  PRINCIPAL  CANALS  OF  THE  U.  S. 
RECLAMATION  SERVICE 


Project 

Name  of  canal 

Size 

Side 
slopes 

Velo- 
city 

Capac- 
ity 

Slope 

N 

Bot- 
tom 
width 

Depth 

Truckee-Carson. 
Truckee-Carson. 
Truckee-Carson. 
Truckee-Carson. 
Truckee-Carson. 
No.  Platte 

Main  Truckee.  .  .  . 
Main  Truckee.  .  .  . 
Lateral  Line  AA.  . 
Lateral  Line  F.  .  .  . 
Lateral  Line  I  .... 

20 
12 

13 

6 

34 
24-5 
30 

22 
23.S 

23 
IS-S 

14-5 
II 

8 
5 

4 
30 
40 
40 
27 
23 
20 
16 
SO 
40 
36.6 
44 
16 
13-0 
n.  8 

27 

40 

20 

13 
13 
6 
3 
3 
10 
10 
9-5 
8.5 

10 

'8 
6 

7 
S 
3 
3 

2 
10 

8.3 
9 
7 
7 
S 
5 
IS 
10 

10 
ii 
6 
5-5 
5-5 
8 
6.5 
9-7 

i|:i 

i   :i 
.2   :i 
2  :i 
2   :i 
I|:i 
2  :i 
|:i 
ij:i 
ij:i 

ij:i 
i|:i 

i|:i 
i*:i 

ii:i 
ij:i 
x|:x 
2   :i 
2  :i 
i   :i 
ij:i 
r|:i 
i   :i 
ii:i 
i   :i 
i   :i 
ii:x 
ij:i 
ij:i 
2  :i 
ij:i 
ii:i 
2  :i 
2   :i 

2.96 
3-70 
2.53 
1.65 
1.73 
2.86 
2-94 
2.75 
2.50 
2.14 

1.89 

2.12 

2.29 
2.60 
2.62 
2.00 
1.52 
2.5 
2.5 
3-08 
2.51 

2-45 
2.47 
2.36 
3-00 
3-27 

3-22 
2.25 

1.74 
2.19 
2.18 
2.70 
2.91 
2.58 

1,520 

1,202 

380 
50 
62 
1,407 
1,220 
908 
738 
824 

529 
312 

401 
240 
98 
56 

21 
1,248 

1,175 
1,358 
659 
575 
307 
278 
2,926 
1,635 
1,659 
1,500 
261 
300 
300 
850 
1,000 
1,000 

0.000154 
o  .  0003 

0.0002 

0.00025 

O.OOO2 

0.00017 
0.00017 
0.00017 
0.00017 

0.0001 
O.OOOI 
0.002 

O.OO02 
O.O004 
0.0008 
0.00055 

0.00055 
0.000135 
0.00015 

0.0002 
0.0002 
O.OOO2 

o  .  0003 

O.OOO3 
O.OOOI 
0.0002 
O.O002 
O.OOOOSl 
O.OOOI32 
0.000201 
0.000193 
O.OOO2 
O.OOO22 
0.00016 

0.025 
0.025 

0.020 
0.02 
O.O2 
0.025 
0.025 
0.025 
O.025 
0.025 

0.025 
0.025 

0.025 
O.O25 
O.O25 
0.025 
0.025 
0.025 
0.025 
0.025 
0.025 
0.025 
O.O25 
O.O25 
0.025 
0.025 
O.O25 
O.025 
0.025 
0.0225 
O.O23 
O.O25 
0.0225 
0.025 

No.  Platte  
No.  Platte  
No.  Platte  
Lower      Yellow- 
stone. 
Lower     Yellow- 
stone. 
Lower      Yellow- 
stone. 
Huntley  
Huntley  
Huntley  

Interstate  

Interstate  2nd.  .  .  . 
Interstate  2nd.  .  .  . 
Main  

Main 

Main  ... 

Main  
Main  

Main 

Huntley  
Huntley  

Main  
Main  
South  

Uncompahgre.  .  . 

Uncompahgre.  .  . 
Belle  Fourche.  .  . 
Belle  Fourche.  .  . 
Belle  Fourche..  . 
Belle  Fourche.  .  . 
Belle  Fourche 

South 

North 

North 

North  

South  

South 

Belle  Fourche.  .  . 
Belle  Fourche.  .  . 
Belle  Fourche.  .  . 
Klamath  
Klamath  
Umatilla  

Waste  Channel  .  .  . 
Inlet...    . 

Inlet  
Main  
E.  Branch  
Feed 

Umatilla  

Feed  

St.  Mary  
Shoshone 

Main  
Garland 

Shoshone  

Garland  

Excavation. — Under  the  term  " excavation"  as  applied  to  canals 
there  is  generally  included  all  earthwork  required  for  the  construc- 
tion of  the  canal,  the  formation  of  embankments,  and  such  other 
incidental  work  as  building  approaches  to  culverts  and  bridges  and 
the  backfilling  around  structures. 

The  excavation  of  canals,  on  account  of  the  relative  magnitude 
of  the  work,  is  one  of  the  most  important  factors  in  the  construc- 
tion of  an  irrigation  system.  The  fundamental  questions  involved 


48        PRINCIPLES  OF  IRRIGATION  ENGINEERING 

in  excavation  are  those  of  cost  and  the  determination  of  methods  by 
means  of  which  the  most  satisfactory  and  economic  results  can  be 
obtained.  There  are  also  involved  the  measurement  and  classi- 
fication of  the  materials  excavated  and  the  direction  of  the  work  in 
such  a  manner  that  the  canal  when  completed  will  serve  as  a  per- 
manent waterway  with  a  minimum  loss  by  seepage  and  cost  for 
maintenance.  Excavation  from  canals  is  commonly  done  either  by 
teams  or  some  form  of  power  excavating  machinery.  The  advantage 
of  either  of  these  methods  over  the  other  depends  largely  upon  the 
character  of  materials  to  be  handled  and  the  local  conditions  affecting 
the  work.  Where  work  is  scattered  over  a  considerable  area,  as 
is  the  case  with  small  canals,  it  is  ordinarily  done  to  best  advantage 
by  means  of  teams  and  scrapers,  or  some  form  of  portable  excavator 
which  can  be  handled  by  teams  or  traction  engines  as  shown  in 
Plate  III. 

When  the  work  is  concentrated  at  one  point  so  as  to  require  but 
little  moving  of  machinery,  as  is  the  case  in  excavating  large  canals 
or  making  deep  cuts,  heavy  excavating  machinery,  such,  for  example, 
as  steam  shovels,  drag-line  scrapers,  or  dredges  are  more  economical 
and  permit  of  better  progress  being  made  than  the  use  of  teams. 
The  amount  of  work  to  be  done  must  also  be  considered  in  determin- 
ing the  most  economic  and  feasible  method.  For  a  small  job 
where  the  cost  of  installing  a  plant  forms  a  large  proportion  of  the 
total  cost  of  the  work  the  unit  cost  by  means  of  machinery  may 
exceed  what  it  would  have  been  with  a  less  expensive  equipment, 
even  though  the  latter  is  less  efficient  in  character,  while  for  a  large 
job  the  cost  of  installation  of  the  more  expensive  and  efficient 
machinery  could  have  been  distributed  over  a  large  amount  of  work 
and  the  unit  costs  correspondingly  decreased.  (See  Plate  IV,  Figs. 
A  and  B.) 

The  distance  which  material  has  to  be  moved  is  also  important 
in  determining  the  method  to  be  used.  For  team  work,  where  the 
haul  does  not  exceed  from  100  to  200  ft.  Fresno  scrapers,  drawn  by 
four  horses,  have  been  found  to  be  the  most  efficient,  while  for 
greater  distances  preference  is  given  to  other  types,  as  for  example, 
the  wheel  scraper.  The  advantage  of  the  latter  is  that  the  hauling 
which  consumes  the  greater  part  of  the  time  can  be  done  with  a  less 
number  of  animals  than  is  required  by  any  form  of  drag  scraper.  It 
is  customary  in  long  hauls  to  use  extra  animals  for  loading  and  de- 
tach them  when  the  loading  is  completed,  allowing  one  team  to 
transport  the  load  to  its  destination.  (See  Plate  II.) 


PLATE  III 


FIG.  A. — Constructing  canal  in  earth  by  means  of  four-horse  Fresno  scrapers. 
Minidoka  Project,  Idaho. 


FIG.  B. — Throwing  up  small  laterals  by  means  of  four-horse  road    machine. 
Huntley  Project,  Mont. 

(Facing  Page  48) 


PLATE  III 


FIG.  C. — Excavating  canal  by  use  of  excavator  with  belt  conveyor,  drawn  by 
traction  engine.     Belle  Fourche  Project,  So.  Dak. 


FIG.  D. — Finished  canal  with  both  upper  and  lower  banks. 

Project,  Mont. 


Lower  YellowsU 


DESIGN  AND  CONSTRUCTION  OF  CANALS          49 

In  building  embankments  team  work  has  an  advantage  over  other 
methods  on  account  of  the  consolidation  of  the  embankments  due 
to  the  tramping  of  the  animals.  When  embankments  to  hold  water 
are  built  by  other  methods  it  is  necessary  to  adopt  some  means  of 
compacting  the  earth.  The  most  common  way  of  doing  this  is  by 
means  of  rolling  or  tamping.  On  account  of  the  difficulty  of  rolling 
small  banks  teams  for  this  class  of  work  are  usually  favored. 

It  must  be  remembered  that  each  particular  job  of  excavation 
differs  in  some  particulars  at  least  from  other  jobs  of  similar  work,  and 
that  methods  which  have  proven  entirely  satisfactory  in  one  case  may 
be  wholly  unsuited  to  another  job.  For  this  reason  it  is  impossible 
to  say  in  general  that  one  method  is  superior  to  another.  In  estimat- 
ing the  cost  of  work  by  a  particular  method  the  safest  plan  is  to 
compare  it  with  the  cost  of  similar  work  elsewhere,  allowance  being 
made  for  difference  in  local  conditions.  Results  obtained  in  this 
manner  are  likely  to  prove  far  more  satisfactory  than  those  based 
upon  theoretical  considerations. 

As  a  basis  for  estimates,  and  the  fixing  of  prices  for  handling 
different  kinds  of  materials,  it  is  customary  to  divide  excavation  into 
classes.  One  method  of  classifying  is  by  natural  designations,  such, 
for  example,  as  earth,  hard  pan,  loose  rock,  solid  rock  and  similar 
terms.  A  second  method  is  to  classify  the  materials  according  to 
the  way  in  which  they  can  be  handled,  as,  for  example,  materials 
which  can  be  plowed,  and  those  which  require  drilling  and  blasting. 
Both  methods  are  to  a  certain  degree  inexact  and  leave  a  great  deal 
to  the  judgment  of  the  engineer. 

In  attempting  to  use  the  method  first  named  it  is  sometimes 
impossible  to  draw  a  sharp  line  of  demarcation  between  the  different 
materials.  The  distinction  between  earth  and  hard  pan  or  even 
between  earth  and  rock  is  not  always  easily  determined  on  account 
of  the  blending  of  one  class  of  material  into  the  other.  It  sometimes 
happens  that  proper  classification  according  to  such  designations 
can  be  made  only  by  a  trained  geologist.  Such  geological  classifica- 
tion may  have  little  practical  value  as  a  measure  of  the  amount  of 
work  required  in  excavation.  Some  material  properly  defined  as 
earth  may  be  more  difficult  and  expensive  to  remove  than  other  ma- 
terial which  may  be  properly  termed  rock. 

The  second  method  of  classification  according  to  some  assumed 
mechanical  operation  avoids  the  use  of  vague  terms,  and  may  depend 
more  nearly  upon  the  amount  of  work,  and  the  resultant  cost 
thereof,  which  will  be  required.  For  example,  material  which  can 


50       PRINCIPLES  OF  IRRIGATION  ENGINEERING 

be  plowed  can  ordinarily  be  handled  with  less  effort  and  at  a  lower 
cost  than  material  which  has  to  be  loosened  by  blasting  or  other 
expensive  operations.  This  method  of  basing  classification  upon 
well-known  and  clearly  defined  operations  for  loosening  or  handling 
materials  has  been  found  the  more  satisfactory.  Differences  of 
opinion  relative  to  such  a  classification  can  ordinarily  be  tested  by 
simple  operations  on  the  work,  thus  avoiding  definitions  which  may 
depend  upon  fine  technicalities. 

Specifications  for  Excavation. — The  construction  of  canals, 
whether  to  be  done  by  contract  or  by  hired  labor  which  is  directly 
under  the  control  of  the  engineer,  should  be  done  in  accordance 
with  definite  plans  and  specifications.  For  contract  work  specifica- 
tions are  necessary  to  define  exactly  what  is  covered  by  the  contract 
and  avoid  all  misunderstanding,  and  where  the  work  is  being  per- 
formed directly  by  hired  force  they  are  of  nearly  equal  importance 
as  a  guide  to  the  superintendents  and  others  in  carrying  out  the 
work.  The  specifications  with  the  plans  of  the  work  should  be 
sufficiently  complete  to  answer  all  ordinary  questions  relative  to 
the  operations  such  as  methods  of  measurement,  payment,  classi- 
fication of  materials,  and  how  the  work  shall  be  handled.  The 
following  specifications,  modified  when  necessary  to  meet  special 
conditions,  are  in  use  by  the  U.  S.  Reclamation  Service: 

(a)  Classification. — All   material   required    to   be   excavated   in 
connection  with  the  construction  of  the  canal  will  be  measured  in 
excavation  and  classified  for  payment  as  follows: 

Class  i.  All  material  that  is  loose  and  can  be  handled  with 
scrapers  and  all  material  that  can  be  plowed  by  a  six-horse  team, 
each  animal  weighing  not  less  than  1,400  lb.,  attached  to  a  suitable 
plow,  all  well  handled  by  at  least  three  men;  also  all  loose  rocks 
in  pieces  not  exceeding  2  cu.  ft.  in  volume  occurring  in  loose  material 
or  in  material  that  can  be  thus  plowed. 

Class  2.  All  material  not  included  in  Classes  i  and  3. 

Class  3.  All  rock  in  place  that  cannot  be  removed  without  the 
use  of  powder  and  all  detached  masses  of  rock  exceeding  10  cu.  ft. 
in  volume. 

(b)  Canal  Section. — The   canal   and  embankment   sections   are 
shown  in   the   drawings,   but   the  undetermined  stability  of  the 
material  that  will  form  the  canal  banks  may  make  it  necessary 
during  the  progress  of  the  work  to  vary  the  slopes  and  the  dimension 
dependent  thereon.     Variations  of  this  character  will  not  entitle 
the  contractor  to  pay  at  any  other  rates  than  those  named  in  the 


DESIGN  AND  CONSTRUCTION  OF  CANALS          51 

contract.  The  canal  shall  be  excavated  to  the  full  depth  and 
width  required  and  must  be  finished  true  to  line  and  grade  in  a 
workman-like  manner.  Earth  slopes  shall  be  neatly  finished  with 
slip  scrapers  or  other  suitable  appliances.  Rock  bottoms  and  banks 
must  show  no  points  of  rock  projecting  more  than  0.3  ft.  in  the 
prescribed  section.  Above  the  water  line  the  rock  will  be 
allowed  to  stand  at  its  steepest  safe  angle,  and  no  finishing  will  be 
required  beyond  removal  of  rock  masses  that  are  loose  and  liable 
to  fall. 

(c)  Material  to  be  Laid  Aside. — Whenever  directed  by  the  engineer 
materials  found  in  the  excavations  such  as  sand,  gravel  or  stone 
that  are  suitable  for  use  in  structures  or  that  are  otherwise  required 
for  special  purposes  shall  be  preserved  and  laid  aside  in  some  con- 
venient place  designated  by  him. 

(d)  Material  for    Canal    Embankments. — All    suitable    material 
excavated  within  the  prescribed  canal  lines  will  be  available  for 
embankment  construction.     So  much  thereof  as  may  be  needed 
shall  be  placed  in  the  embankment  where  directed  by  the  engineer. 
Where  this  source  of  material  is  inadequate  additional  material 
may  be  obtained  from  borrow  pits  whose  location  will  be  subject 
to  the  approval  of  the  engineer.     Unless  the  engineer  gives  the 
contractor  specific  written  orders  to  excavate  other  than  Class  i 
material  from  borrow  pits  for  embankment  construction  all  material 
obtained  from  this  source  for  such  purpose  will  be  paid  for  at  the 
unit  price  bid  for  Class  i  regardless  of  its  actual  character. 

(e)  Construction  of  Embankments. — The  ground  under  all  embank- 
ments that  are  to  sustain  water  pressure  shall  be  cleared  of  brush, 
trees  and  roots.     The  foundation  surface  shall  be  well  plowed. 
Should  the  engineer  direct  that  unsuitable  material  be  excavated 
and  removed  from  the  site  of  the  embankment  the  material  thus 
excavated  will  be  paid  for  as  excavation.     All  material  deposited 
in  embankments  that  are  to  sustain  water  pressure  shall  be  thor- 
oughly compacted.     The  compacting  must  be  equivalent  to  that 
obtained  by  trampling  of  well-distributed  scraper  teams  depositing 
the  material  in  layers  that  are  6  in.  thick  when  compacted. 

(f)  Runways. — Runways  shall  not  be  cut  into  canal  excavation 
slopes  below  the  proposed  water  level, 

(g)  Blasting. — Any   blasting   that   would   injure   the   work   will 
not  be  permitted.     If  the  slopes  are  shattered  or  broken  by  blasting, 
such  places  shall  be  excavated  to  firm  material,  and  the  holes  thus 
made  shall  be  filled  to  grade  or  slopes  with  such  material  and  in 


52        PRINCIPLES  OF  IRRIGATION  ENGINEERING 

such  manner  as  the  engineer  may  designate,  all  at  the  expense  of 
the  contractor. 

(h)  Excess  Excavation. — Material  excavated  for  the  canal  in 
excess  of  that  required  for  canal  embankments  shall  be  used  for 
the  widening  of  the  embankments  as  may  be  directed  by  the  engineer. 
Material  taken  from  cuts  that  is  not  suitable  for  embankment 
construction  and  other  material  not  required  for  embankments  or 
embankment  widening  may  be  wasted  on  the  right-of-way  owned 
by  the  United  States,  provided  it  is  not  deposited  in  drainage 
channels  nor  within  25  ft.  of  the  edge  of  the  canal  cut. 

(i)  Overhaul. — In  hauling  excavated  material  required  for  embank- 
ments or  other  useful  purposes  or  for  laying  aside  for  subsequent 
use,  200  ft.  will  be  considered  the  limit  of  free  haul  and  any  haul 
in  excess  of  this  distance  will  be  termed  overhaul.  Whenever  the 
engineer  requires  such  material  to  be  hauled  more  than  200  ft., 
the  contractor  will  be  paid  for  overhaul  at  the  rate  of  one  and  one- 
half  cents  per  cubic  yard  per  100  ft.  for  the  haul  in  excess  of  200  ft. 
No  overhaul  of  material  wasted  will  be  paid  for. 

(j)  Measurement  and  Payment. — Measurement  will  be  made 
to  the  neat  lines  of  the  excavation  as  shown  on  drawings  or  staked 
out  by  the  engineer.  Payment  for  excavation  will  be  made  at  the 
unit  price  bid  therefor  which  shall  include  the  cost  of  all  labor 
material  and  supplies  incident  to  excavating  and  placing  the  material 
in  embankments,  preparing  surface,  spreading,  rolling,  tamping,  etc., 
required  to  complete  the  work  in  accordance  with  the  specifications. 

Protection  Against  Seepage  in  Canals. — The  losses  of  water  in 
transmission  in  a  canal  system,  especially  one  recently  constructed, 
form  a  notable  proportion  of  the  amount  of  water  received  into 
the  canal.  Careful  observations  and  studies  should  be  made  of 
these  losses  in  order  to  ascertain  where  they  are  taking  place  and 
to  take  measures  for  their  correction,  not  merely  to  prevent  the 
loss  of  the  water  which  is  valuable  in  itself,  but  to  keep  this  seepage 
water  from  ruining  lands  in  the  vicinity.  The  amount  of  these 
losses  is  illustrated  by  the  accompanying  figure  which  gives  for 
comparison  the  total  diversions  from  the  river  in  each  case,  and  the 
proportion  of  this  which  is  lost  in  transmission. 

The  accompanying  figure  (12)  gives  for  the  months  of  April  to 
September  or  October  the  quantity  of  water  which  was  received 
into  the  canal,  this  being  indicated  by  the  vertical  spaces  and  the 
quantity  which  is  lost  in  transit.  This  is  classified  in  most  cases 
into  the  losses  in  the  main  canal  and  those  in  the  lateral  system. 


DESIGN  AND  CONSTRUCTION  OF  CANALS     -     53 


Su 

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Umatilla  Project  Or 
,\on«    from    R1*«      »"d 

agon 

200s.f. 

^"^"--"  p[i^ 

100s.f. 
Os.  f. 

^^ 

April 

Ma,               June 

Jul, 

Aug. 

SepU 

200s.  f. 

Tie 

toil  Project  -  Washington 

^L     s 

1 

100s.  f. 

^^vj^-u,.   and    ItMj^ 

in  Lateral  S,sUn>>^^ 

n«  f 

Ma,        |        Jun«       I        Jul,               Aug. 
Note:-Praticallyno  Losses  In  Main  Canal 

Sept. 

FIG.  12. — Diagram  illustrating  relative  quantities  of  water  used,  and  lost 
in   laterals   and   in   main   canals   of  various  projects  during  the  crop  season 

Of    IQII. 


54    .    PRINCIPLES  OF  IRRIGATION  ENGINEERING 

It  is  to  be  noted  that  in  general  the  losses  are  in  proportion  to  the 
quantity  diverted,  although  theoretically  at  least  the  losses  during 
the  early  part  of  the  season  should  be  greater  in  proportion  to  those 
later  on. 

Where  it  is  necessary  to  use  unsatisfactory  material  for  the  con- 
struction of  canal  banks,  or  where  canals  are  excavated  in  loose  or 
porous  material,  special  precautions  have  to  be  taken  against  loss  of 
water  by  seepage.  'Seepage  from  canals  may  be  either  through  the 
sides  and  bottom  under  the  artificial  banks,  or  through  the  embank- 
ments themselves.  Where  it  is  of  the  first  form  it  frequently  pene- 
trates to  some  depth  in  the  natural  material  and  comes  to  the  surface 
at  a  considerable  distance  from  the  canal.  Seepage  of  this  kind  is 
the  most  difficult  to  prevent.  It  can  sometimes  be  avoided  by  cut- 
ting a  deep  trench  underneath  the  canal  embankment  and  filling  it 
with  puddle  or  other  impervious  material.  Where  this  method  is 
employed  it  is  necessary  to  carry  the  core  down  to  impervious 
material  which  can  frequently  be  done  on  side-hill  work. 

Another  method  of  preventing  seepage  is  to  cover  the  slopes  and 
bottom  of  the  canal  with  fine  material,  such  as  soil  or  loam,  which, 
when  acted  upon  by  the  water  is  carried  into  the  interstices  of  the 
material  below  in  time  forming  a  water-tight  film  along  the  surface. 

The  remedies  for  seepage  through  artificial  banks  are  practically 
the  same  as  those  above  mentioned,  i.e.,  by  constructing  a  core  of 
puddle  or  other  impervious  material  in  the  center  of  the  bank,  or  by 
lining  the  inner  slope  with  soil  or  other  fine  material. 

Where  a  canal  is  lined  to  prevent  seepage,  care  must  be  taken  in 
future  maintenance  and  cleaning  of  the  canal  to  avoid  removing 
or  breaking  into  this  thin  layer  of  water-tight  material. 

In  the  construction  of  canals  much  can  be  done  to  prevent  seepage 
through  the  banks  by  requiring  that  the  coarse  material  be  placed 
on  the  outer  portion  and  the  finer  material  on  the  inner  side  of  the 
banks.  In  the  construction  of  canals  in  cold  climates,  especial  care 
should  be  taken  to  see  that  material  is  not  deposited  while  the  mate- 
rial or  the  embankment  is  frozen.  When  in  a  frozen  condition, 
material,  especially  if  it  be  moist,  occupies  a  greater  space  than  after 
it  is  thawed,  and  in  the  process  of  thawing  is  likely  to  leave  small 
openings  through  which  water  can  escape. 

Another  method  for  preventing  seepage  which  is  sometimes  re- 
sorted to  is  by  lining  the  canal  either  with  masonry,  plaster  or 
lumber. 

On  one  of  the  Reclamation  Service  canals,  where  it  was  necessary 


PLATE  IV 


FIG.   A. — Enlarging  canal  by  means  of  floating    dipper  dredge. 

Project,  Ariz. 


Salt  River 


FIG.  B. — Enlarging  canal  by  use  of  excavator  with  drag-line  working  from  one 

side  of  canal.     Salt  River  Project,  Ariz. 

(Facing  Page  54) 


PLATE  IV 


FIG.  C. — Lining  canal  with  concrete  to  increase  the  capacity,  and  reduce  the 
seepage.     Boise  Project,  Idaho. 


Fir,.  1).  -Concri'te  lined  canal  in  shattered  rock,  carrying  water  of  Truckee  River 
to  Carson  River.    Truckee-Carson  Project,  Nev. 


DESIGN  AND  CONSTRUCTION  OF  CANALS          55 

to  carry  water  through  a  canal  constructed  on  a  large  fill,  a  temporary 
lining  of  lumber  was  constructed  to  be  used  until  the  embankment 
should  become  thoroughly  settled.  The  future  plans  provide  that 
when  such  settlement  has  taken  place  and  the  lining  must  be  re- 
newed it  will  be  replaced  by  some  form  of  permanent  material. 

Seepage  sometimes  results  from  erosion  of  banks  by  which  the 
finer  material  along  the  surface  is  carried  away.  This  is  most  likely 
to  occur  on  the  outer  slope  around  curves. 

Lined  Canals. — In  the  construction  of  canals  a  permanent  lining 
of  concrete  is  frequently  used.  The  purpose  of  such  a  lining  is  two- 
fold; first,  to  prevent  seepage  where  a  canal  is  constructed  in  porous 
material;  and  second,  to  increase  the  velocity  and  thus  reduce  the 
section  of  the  canal  where  deep  cutting  is  required.  If,  for  example, 
a  canal  is  to  be  constructed  to  a  depth  two  or  three  times  that  of  the 
depth  of  the  water  it  is  frequently  cheaper  to  excavate  a  smaller 
section  and  line  the  lower  wetted  portion  than  to  excavate  a  canal 
having  the  required  capacity  in  earth  section.  Where  concrete 
lining  is  used,  it  is  economical  to  make  the  side  slopes  as  steep  as 
possible.  As  shown  on  page  39,  the  most  advantageous  section 
theoretically  is  one  with  vertical  slopes.  This,  however,  is  impracti- 
cable. It  frequently  happens,  however,  in  deep  cuts  that  material 
will  stand  on  as  steep  slopes  as  1/2  horizontal  to  i  vertical,  which 
is  a  section  very  commonly  used  in  lined  canals.  In  placing  the 
lining  in  canals  with  slopes  as  great  as  1/2  to  i,  it  is  ordinarily  neces- 
sary to  use  forms  on  the  inner  slope,  filling  in  the  concrete  between 
the  forms  and  the  earth  or  rock  banks.  Where  the  excavation  is 
taken  out  beyond  the  neat  lines  this  space  can  be  backfilled  with 
loose  rock.  In  placing  lining  on  slopes  i  horizontal  to  i  vertical, 
or  flatter,  it  is  possible  to  do  the  work  without  the  use  of  forms. 
(See  Plate  IV,  Fig.  6.) 

Canal  linings  are  usually  constructed  in  slabs  of  from  10  ft.  or  more 
in  width  built  in  alternate  sections  so  as  to  provide  expansion  joints 
and  prevent  temperature  cracks.  Paper,  or  a  thin  painting  of  oil,  is 
sometimes  applied  to  the  edge  of  the  slabs  to  prevent  the  concrete 
bonding.  This  protection,  however,  is  ordinarily  unnecessary  if  the 
concrete  in  the  first  slabs  is  allowed  to  set  before  the  second  is  put  in. 
The  thickness  of  concrete  used  for  a  permanent  canal  lining  varies 
from  3  to  6  in.,  depending  upon  the  steepness  of  the  slopes,  the 
nature  of  the  material,  and  climatic  conditions.  Freezing  has  a 
tendency  to  loosen  the  lining  from  the  banks  by  the  expansion  due 
to  crystallization  of  the  small  amount  of  water  in  the  earth.  In  a 


56       PRINCIPLES  OF  IRRIGATION  ENGINEERING 

cold  climate,  where  freezing  is  likely  to  penetrate  the  lining,  the 
customary  thickness  for  conditions  of  this  kind  is  about  6  in.  In 
climates  where  frost  is  not  prevalent  a  less  thickness  is  sufficient. 
Linings  sometimes  fail  on  account  of  the  pressure  exerted  by  water 
which  collects  behind  them.  This  can  be  relieved  by  putting  weep 
holes  through  the  bottom  of  the  lining  at  frequent  intervals.  The 
construction  of  weep  holes  is  also  an  additional  protection  against 
frosts  as  they  keep  the  material  back  of  the  lining  drained  and  re- 
duce the  amount  of  expansion  when  freezing  occurs. 


FIG.  13. — Cement  lined  canal  with  reenforced  concrete  arch  cover  later  added 
to  catch  the  loose,  sliding  debris  from  steep  hill  slopes,  Strawberry  Valley  Proj- 
ect, Utah. 


Roadways  on  Banks. — Roadways  on  the  banks  of  canals  have  cer- 
tain advantages,  in  that  they  permit  of  easy  access  to  the  canal  for 
operation  and  maintenance  purposes.  In  highly  cultivated  areas, 
where  land  is  valuable,  there  is  a  saving  of  the  land  that  would 
otherwise  be  required  in  the  location  of  highways.  There  is  also  a 
certain  gain  due  to  the  compacting  effect  of  travel  on  the  banks. 
This  latter,  however,  is  of  little  value  except  on  new  canals. 

The  disadvantages  of  roadways  constructed  on  canal  banks  are 
that  with  certain  materials  the  traffic  has  a  tendency  during  the  dry 
season  to  break  up  the  surface  layers  into  dust,  rapidly  carried  away 


DESIGN  AND  CONSTRUCTION  OF  CANALS          57 

by  the  winds.  There  is  a  tendency  also  to  wearing  down  of  the 
banks  into  ruts  which,  during  the  rainy  season,  become  filled  with 
water  which  finally  breaks  over  the  banks  and  causes  erosion  of  the 
slopes. 

The  practicability  of  constructing  roadways  on  the  banks  of 
canals  in  general  depends  upon  the  local  conditions,  all  of  which 
must  be  taken  into  account  in  determining  the  proper  course  to 
pursue.  Where  roadways  are  constructed  on  banks  it  is  necessary 
to  make  the  top  width  somewhat  greater  than  would  be  required  if 
such  roadways  were  not  built.  '  In  ordinary  materials  banks  made 
with  a  top  width  of  about  10  ft.  are  usually  strong  enough  to  with- 
stand the  water  pressure.  Where  a  roadway  is  required  on  the 
bank,  the  top  width  should  be  not  less  than  12  ft.  and  preferably 
from  14  to  1 6  ft.  In  a  climate  where  snow  and  ice  prevail  during  a 
portion  of  the  year  roadways  upon  banks,  except  of  considerable 
width,  are  dangerous  and  should  be  avoided  for  public  travel. 

Lateral  Drainage. — In  order  to  provide  full  protection  for  a  canal, 
especially  when  located  on  sloping  ground,  it  is  necessary  to  provide 
for  the  care  of  lateral  drainage.  This  feature,  if  neglected,  may 
cause  pools  to  form  above  the  canal  and,  in  periods  of  extreme 
rainfall,  may  result  in  an  overtopping  of  the  banks.  The  amount 
of  lateral  drainage  which  must  be  taken  care  of  is  a  question  some- 
what difficult  to  determine.  Especial  study  must  be  given  to  each 
particular  case.  The  most  satisfactory  method  of  determining  the 
amount  of  lateral  drainage  in  a  particular  waterway  is  by  past 
records  of  the  quantity  of  flow.  Information  of  this  kind,  however, 
is  generally  lacking,  as  flood  conditions  in  ravines  or  small  streams 
which  are  to  be  crossed  by  an  irrigation  canal  are  generally  not 
observed.  It  is  sometimes  possible  to  determine  from  water  marks 
the  area  of  cross-section  of  a  stream  and  from  the  general  slopes  of 
the  country  to  form  some  estimate  of  the  velocity  and  corresponding 
amount  of  discharge.  Where  such  data  are  available  they  serve  as 
a  guide  in  determining  the  amount  of  drainage  water  which  must  be 
cared  for. 

Where  all  information  relative  to  flow  is  lacking  an  estimate  of 
the  amount  of  runoff  can  be  made  from  the  catchment  area,  assuming 
a  maximum  rainfall  per  square  mile.  The  amount  of  rainfall  which 
must  be  assumed  in  this  case  will  vary  greatly  in  different  parts  of 
the  country.  The  size  of  the  drainage  area  is  also  a  factor  in  deter- 
mining the  runoff  per  unit  area,  since,  on  small  areas,  the  water  is 
more  quickly  collected  and  approximates  more  closely  to  the  total 


58        PRINCIPLES  OF  IRRIGATION  ENGINEERING 

amount  of  rainfall  on  the  area.  For  small  areas,  say,  for  example, 
from  i  to  5  square  miles,  the  maximum  runoff  for  a  given  period  may 
reach  approximately  the  total  amount  of  water  falling  on  the  catch- 
ment area  during  the  period.  This,  however,  is  exceptional.  In 
providing  for  lateral  drainage  for  the  protection  of  canals  it  is  neces- 
sary to  consider  extreme  cases,  and  good  practice  demands  that 
errors  be  on  the  side  of  safety  in  providing  for  a  greater  runoff 
than  is  necessary,  rather  than  one  which  is  too  small  for  maximum 
conditions. 

Lateral  drainage  may  be  cared  for  by  diverting  the  water  into  the 
canal,  or  carrying  it  under  or  over  the  canal.  The  method  which  is 
most  desirable  in  any  particular  case  will  depend  upon  local  condi- 
tions. Where  the  quantity  of  lateral  drainage  is  small  and  where 
it  does  not  occur  during  the  irrigation  season  it  is  frequently  possible 
to  carry  it  into  the  canal  and  dispose  of  it  through  some  wasteway 
into  natural  channels.  When  lateral  drainage  must  be  provided 
for  during  the  irrigation  season  this  method  is  unsafe  on  account 
of  the  danger  of  exceeding  the  capacity  of  the  canal.  The  method 
of  diverting  drainage  into  a  canal  is  ordinarily  by  means  of  a  flume 
or  shallow  channel  down  the  upper  slope  of  the  canal. 

Where  the  quantity  of  drainage  is  not  excessively  large,  it  may  be 
diverted  under  the  canal  by  means  of  a  siphon  or  culvert.  This 
method  is  particularly  well  adapted  to  locations  where  the  canal 
is  constructed  in  fill  thus  permitting  a  siphon  or  culvert  to  be  con- 
structed beneath  the  canal  with  a  minimum  amount  of  excavation. 
The  upper  bank  in  such  a  case  also  provides  a  small  amount  of 
storage  which  helps  to  control  the  drainage  water.  The  filling  up 
of  the  depression  above  the  canal  also  raises  the  head  on  the  cul- 
vert or  siphon  and  increases  its  capacity  during  a  flood. 

Where  large  quantities  of  drainage  water  must  be  taken  under  a 
canal  a  common  practice  is  to  carry  the  canal  in  a  flume  supported 
by  means  of  a  suitable  bridge  or  trestle  work.  In  the  location  and 
design  of  a  structure  of  this  kind  especial  care  should  be  taken  to 
see  that  the  opening  below  the  structure  is  sufficiently  large  to 
provide  for  the  maximum  flow.  A  good  example  of  a  large  canal 
being  carried  across  a  draw  is  the  Spring  canyon  flume  on  the  North 
Platte  project,  Nebraska.  Here  a  canal  of  i  ,400  second-feet  capacity 
is  carried  over  a  canyon  by  means  of  a  concrete  flume  supported  by 
three  reinforced  concrete  arches.  The  span  of  the  largest  arch  is  50 
ft.  and  the  total  distance  spanned  no  ft.  (See  Plate  VII,  Fig.  A.) 

The  third  method  of  caring  for  lateral  drainage,  by  taking  it  over 


DESIGN  AND  CONSTRUCTION  OF  CANALS          59 

a  canal,  may  be  accomplished  by  employing  a  flume  or  other  struc- 
ture for  carrying  the  drainage  water,  or  by  carrying  the  canal 
beneath  the  natural  drainage  channel  by  means  of  an  inverted 
siphon. 

In  general,  where  the  quantity  of  lateral  drainage  is  small,  it  may 
be  taken  care  of  by  drainage  into  the  canal  or  by  a  flume  or  culvert 
constructed  either  under  or  over  the  canal.  Where  the  quantity  is 
large,  however,  or  where  the  drainage  area  is  considerable  in  amount, 
the  better  and  safer  plan  is  to  allow  the  drainage  to  follow  its  natural 
waterway  and  to  divert  the  canal  either  under  or  over  the  stream. 

Right-of-way  for  Canals. — The  cross-section  and  location  of  a 
canal  having  been  fixed,  the  width  of  right-of-way  required  can  be 
determined.  On  account  of  the  ordinarily  high  values  of  irrigable 
lands  it  is  desirable  that  no  more  be  taken  for  right-of-way  than  is 
necessary,  while,  on  the  other  hand,  it  is  essential  that  sufficient 
width  be  procured  to  permit  economical  operation  and  maintenance. 
The  width  of  right-of-way  required  depends,  to  a  great  extent,  upon 
the  size  and  importance  of  a  canal.  For  main  canals  the  right-of- 
way  should  be  wide  enough  to  include  all  embankments  and  in  gen- 
eral with  sufficient  additional  width  to  permit  of  work  being  done 
on  these  embankments  without  trespassing  on  adjacent  property. 

The  right-of-way  should  provide,  especially  in  the  vicinity  of 
embankments,  a  certain  amount  of  space  which  can  be  used  for  bor- 
row pits  in  case  of  emergency.  The  successful  operation  of  a  canal 
system  or  of  a  canal  may  depend  upon  having  immediately  avail- 
able material  for  making  repairs.  Unless  provision  is  made  for  this 
when  the  original  right-of-way  is  acquired,  there  is  no  assurance 
in  future  years  that  needed  material  can  be  had  at  once.  As  lands 
are  irrigated  and  the  country  becomes  more  thickly  settled  the  value 
of  land  and  the  difficulties  of  acquiring  additional  right-of-way 
increase  correspondingly. 

The  right-of-way  for  small  and  less  important  canals  may  be 
narrower  than  for  larger  canals.  In  every  case,  however,  the  right- 
of-way  should  be  sufficient  to  provide  for  access  along  the  canal  for 
repairs  and  for  needed  materials  for  maintaining  fills.  For  a  small 
lateral,  located  practically  all  in  cut  and  over  comparatively  level 
ground,  the  only  right-of-way  required  in  addition  to  the  waterway 
is  that  necessary  for  travel  along  the  canal.  The  same  size  canal 
located  upon  uneven  ground  or  over  a  high  fill  would  require  a  con- 
siderable amount  of  additional  right-of-way  in  order  to  provide  for 
material  for  repairing  breaks  in  case  of  emergency. 


60        PRINCIPLES  OF  IRRIGATION  ENGINEERING 

There  can  be  no  fixed  rule  laid  down  as  to  the  width  of  right-of-way 
which  is  required  for  any  particular  size  canal.  It  must  be  kept  in 
mind  that  for  successful  operation  it  is  necessary  to  have  unrestricted 
access  to  every  portion  of  the  canal  system,  and  that  for  economical 
maintenance  there  is  need  of  sufficient  room  for  operation  and  of 
material  for  repairing  breaks  in  case  of  an  emergency. 

Rights-of-way  are  of  two  classes:  first,  those  which  permit  of  the 
land  being  used  for  canal  purposes,  the  fee  or  actual  title  thereof 
remaining  with  the  original  owner;  and,  second,  ownership  in  fee 
simple.  Ordinarily  a  title  to  a  right-of-way  which  permits  of  the 
construction  and  operation  of  a  canal  only  is  objectionable,  on  account 
of  certain  rights  which  the  original  owner  of  the  land  may  have 
thereto.  For  this  reason  it  is  believed  that  rights-of-way  for  main 
canals  should  be  purchased  outright  so  that  the  canal  owners  will  be 
free  to  handle  the  construction  and  future  operation  and  mainte- 
nance without  restriction. 


CHAPTER  V 
CANAL  STRUCTURES 

Classification. — Under  the  term  "Canal  Structures"  are  usually 
included  all  appurtenances  outside  of  the  main  waterway  of  the  canal 
together  with  any  devices  necessary  for  carrying  the  main  waterway 
over  or  under  streams,  such,  for  example,  as  flumes,  siphons,  etc. 
In  accordance  with  the  purpose  for  which  they  are  intended,  canal 
structures  may  be  classified  under  three  heads,  as  follows: 

1.  Structures  for  diversion  and  controlling  of  water. 

2.  Structures  for  protection. 

3.  Miscellaneous  structures. 

Under  the  first  classification,  structures  for  diversion  and  control- 
ling of  water,  are  included  head  gates,  which  regulate  the  amount 
of  water  diverted  into  a  canal;  turnouts,  for  controlling  and  regu- 
lating the  amount  of  water  diverted  from  a  canal,  and  checks  and 
drops,  which  regulate  the  surface  elevation  of  water  in  a  canal. 

Under  the  second  classification,  structures  for  protection,  are 
included  wasteways  for  discharging  excess  waters  from  a  canal  to 
prevent  its  being  burdened  above  its  normal  capacity  and  also  for 
emptying  the  canal  in  cases  of  emergency.  There  are  included  in 
this  class  also  culverts  and  other  structures  intended  to  remove  excess 
waters  from  the  canal  and  prevent  the  banks  being  overtopped. 

Under  the  head  of  miscellaneous  structures  are  included  bridges 
and  like  structures  made  necessary  by  the  presence  of  the  canal. 
Structures  of  the  latter  class  may  or  may  not  have  a  part  in  the  op- 
eration or  maintenance  of  a  canal  and  are  not  necessarily  a  part  of 
the  canal  system.  They  are  necessary,  however,  for  the  use  of 
individuals  or  the  public  in  general  to  compensate  for  the  inconveni- 
ence caused  by  the  construction  of  the  canal  and  must  therefore  be 
considered  as  a  part  of  the  appurtenances  of  such  canal. 

Permanent  and  Temporary  Structures. — Canal  structures  are 
sometimes  also  classified  as  temporary  and  permanent.  A  perma- 
nent structure  is  one,  the  location  and  duties  of  which  are  sufficiently 
well  known,  that  can  be  built  of  lasting  materials  and  in  such  a  man- 
ner as  to  serve  during  the  life  of  such  materials.  A  temporary  struc- 
ture is  one,  the  location  or  purpose  of  which  has  not  been  definitely 

61 


62        PRINCIPLES  OF  IRRIGATION  ENGINEERING 

determined  or  one  which  on  account  of  future  developments,  will 
be  rendered  useless  and  can  be  removed  at  the  end  of  a  short  period. 

In  the  laying  out  and  construction  of  distribution  systems  it  is 
frequently  advisable  to  provide  temporary  measures  for  delivering 
water  on  certain  areas  before  final  work  is  completed.  In  such  cases 
the  use  of  temporary  structures  is  justifiable.  It  frequently  happens 
also  that  changes  in  the  methods  of  irrigation  will  be  made,  which, 
when  effected,  will  require  different  modes  or  points  of  delivery. 
In  such  cases  the  use  of  temporary  structures  is  also  justifiable. 

In  the  design  and  location  of  structures,  especially  those  pertain- 
ing to  the  delivery  of  water,  it  must  be  remembered  that  irrigation 
is  not  yet  developed  to  the  point  of  an  exact  science  and  that  specific 
cases  will  be  encountered  upon  which  we  have  little  or  no  previous 
experience  and  where  the  choice  between  two  different  methods  is 
difficult.  In  cases  of  this  kind  it  is  frequently  justifiable  to  construct 
works  of  a  temporary  character  to  be  utilized  in  a  somewhat  experi- 
mental manner  until  the  proper  data  for  location  and  construction 
of  permanent  works  can  be  obtained.  Except  in  such  cases  as  above 
mentioned,  which  it  is  believed  are  generally  rare,  structures  so  far 
as  consistent  with  cost  should  be  made  of  as  permanent  a  character 
as  possible  in  order  that  they  may  afford  ample  protection  to  the 
system  during  the  period  of  its  operation. 

Headgates. — The  function  of  a  headgate  is  to  control  and  regu- 
late the  discharge  of  water  into  canals.  The  term  "headgate"  is 
generally  applied  to  the  larger  structures,  such,  for  example,  as 
those  at  the  head  of  main  canals  or  laterals.  The  requirements 
for  headgates  for  a  canal  are  as  follows:  First,  they  shall  be  strong 
enough  to  withstand  the  maximum  pressure  and  head  of  water 
which  is  imposed  upon  them;  second,  they  shall  have  sufficient 
capacity  to  divert  the  maximum  flow  of  the  canal ;  third,  they  shall 
permit  of  regulation  sufficient  to  control  with  accuracy  the  quantity 
of  water  being  diverted. 

In  the  design  of  a  headgate  first  consideration  should  be  given 
to  the  question  of  its  stability.  On  a  large  or  important  canal  the 
headgates  serve  as  a  protection  for  the  canal  system  and  property 
thereunder.  On  account  of  this  important  function  no  pains  should 
be  spared  in  the  design  and  location  of  such  structures  to  make  them 
absolutely  safe,  and  of  as  permanent  a  character  as  is  consistent 
with  reasonable  expenditure.  Permanent  headworks  on  important 
canals  are  usually  constructed  of  masonry,  the  ordinary  type  of 
design  being  some  form  of  gravity  structure  amply  heavy  to 


PLATE  V 


FIG.  A, — Wooden  headgates,  typical  of  those  usually  built  for  the  earlier  canals. 
Jordan  and  Salt  Lake  City  Canal,  Utah. 


FIG.  B.  —  Concrete  head  works  with  steel  gates. 

Project,  Nebr. 


Interstate  canal,  North  Platte 


(Facing  Page  62) 


PLATE  V 


FIG.  C. — Concrete  headworks  and  roadway,  Mesilla  Valley  canal.     Rio  Grande 

Project,  N.  Mex. 


FIG.  D. — Concrete  headworks  with  sluice  gates  at  Laguna  dam  on  Colorado 

River,  Ariz.-Cal. 


CANAL  STRUCTURES 


63 


Section  7-jK" 


Section 


FIG.  14. — Head-works  for  Interstate  Canal,  North  Platte  Project, 
Wyoming-Nebraska. 


64        PRINCIPLES  OF  IRRIGATION  ENGINEERING 


CANAL  STRUCTURES  65 

resist  overturning  with  the  maximum  head  which  may  be  imposed 
upon  it. 

Another  important  factor  in  the  design  and  construction  of  head- 
works  is  to  provide  sufficient  curtain  and  wing  walls  to  prevent 
seepage  either  under  or  around  the  structure.  The  extent  of  such 
protection  against  seepage  will  depend  upon  the  amount  of  head  and 
the  character  of  material  in  which  the  structure  is  placed  and  no 
general  rules  can  be  laid  down  for  designs  of  this  kind.  It  is,  however, 
essential  that  a  complete  study  and  investigation  be  made  in  each 
particular  case. 

In  backfilling  around  headgates  the  greatest  care  should  be  given 
both  to  the  character  and  manner  of  compacting  the  material. 
Under  ordinary  conditions  the  greatest  degree  of  compactness  can 
be  obtained  by  the  use  of  water,  that  is,  by  either  wetting  the  mate- 
rial to  a  slight  degree  and  tamping  it  or  by  depositing  it  in  water. 

The  capacity  of  a  headgate  should  be  computed  not  only  for  the 
maximum  capacity  of  the  canal  but  for  various  stages  of  water  both 
above  and  below  the  headgates.  It  is  frequently  necessary,  espe- 
cially where  a  water  supply  is  limited,  to  operate  a  canal  at  part 
capacity.  Where  this  is  necessary  a  headgate  should  be  so  designed 
that  the  full  capacity  of  the  canal  up  to  any  level  can  be  drawn  from 
the  source  of  supply  without  undue  loss  of  head  at  the  structure. 
In  determining  these  functions  it  is  necessary  to  consider  both  veloc- 
ity and  entry  head  and  the  entry  coefficient.  These  principles 
apply  especially  where  diversions  are  made  from  fluctuating  heads 
as,  for  example,  from  streams  without  ample  diversion  weirs. 

Operating  Device. — The  essential  characteristics  of  the  operating 
device  are  that  it  be  simple  in  operation  and  capable  of  controlling 
accurately  the  amount  of  the  discharge.  Various  forms  of  control- 
ling devices  are  in  use.  They  vary  from  the  simple  flash  boards 
which  may  be  operated  by  hand  to  carefully  designed  and  con- 
structed metal  gates  operated  by  means  of  electric  or  other  power. 
On  account  of  the  difficulty  of  operation,  the  flash-board  control  is 
not  recommended  for  important  diversion  points. 

The  type  of  controlling  apparatus  which  appears  most  satis- 
factory for  main  canals  and  which  is  rapidly  replacing  the  older  type 
of  flash  board  or  wooden  gates  recently  built  in  irrigation  systems 
is  some  form  of  metal  gate  operated  by  a  screw  driven  by  hand  or 
machine  power  as  shown  in  Fig.  15.  The  advantages  of  a  device 
of  this  kind  are  that  it  is  susceptible  of  a  slight  motion  and  furnishes 
the  means  for  regulation  to  any  desired  quantity.  Whether  or  not 


66        PRINCIPLES  OF  IRRIGATION  ENGINEERING 

power  is  necessary  depends  upon  the  amount  of  energy  necessary  to 
be  expended  and  the  time  required  for  opening  or  closing  the  gates. 
A  satisfactory  conclusion  on  this  point  can  be  made  only  by  careful 
computations.  To  take  a  concrete  example,  we  will  consider  a  gate 
5  ft.  square,  subjected  to  a  maximum  head  of  20  ft.  at  its  central 
point.  The  total  pressure  on  the  gate  will  be  p  =  62. 5X25X20  = 
31,250  Ib.  Assuming  the  coefficient  of  friction  between  the  gate 
and  guides  to  be  0.25,  the  total  force,  .exclusive  of  the  weight  of  the 
gate  and  stem,  required  to  start  it  from  a  position  of  rest  will  be  0.25 
X 3 1, 2 50  =  7, 8 1 2. 5  Ib.  To  raise  this  gate  at  the  rate  of  i  ft.  per 


FIG.  1 6. — Electrically  operated  sluice  gates,  Salt  River  Project,  Arizona. 

minute,  if  we  assume  the  weight  of  the  gate  to  be  say  3,000  Ib.,  will 
require  the  expenditure  of  10,800  ft.-lb.  of  energy  per  minute  or 
approximately  1/3  h.p. 

In  some  cases,  where  the  water  supply  carries  large  quantities  of 
silt  in  suspension  which  it  is  desirable  to  prevent  entering  the  canals, 
special  forms  of  headgates  or  diversion  works  are  used.  The  most 
common  method  of  preventing  silt  from  entering  the  canals  is  by 
skimming  the  water  from  the  surface  thus  leaving  the  heavy  silts 


CANAL  STRUCTURES  67 

which  are  carried  nearer  the  bottom  undisturbed.  To  accomplish 
this,  flash  boards,  the  top  portion  of  which  can  be  removed,  or  gates 
which  can  be  lowered  so  as  to  allow  the  water  to  pass.over  them,  are 
used.  Where  this  form  of  diversion  is  employed  it  is  necessary  to  con- 
struct sluice  gates  for  removing  the  silts  which  are  deposited  above 
the  headgates.  These  sluice  gates,  in  order,  to  be  effective,  should  be ' 
placed  near  the  diversion  gates  and  should  also  be  at  a  considerably 
lower  elevation. 

The  diversion  works  at  theLaguna  Dam  near  Yuma,  Arizona,  shown 
on  Plate  V,  Fig.  D,  consist  of  a  series  of  overflow  gates  of  sufficient 
width  that  the  supply  is  drawn  from  the  upper  4  ft.  of  the  pool  above 
the  dam.  The  accumulated  silts  are  removed  by  means  of  sluice- 
ways, the  bottoms  of  which  are  approximately  13  ft.  below  the  top  of 
the  dam.  These  sluiceways  are  controlled  by  means  of  electrically 
operated  gates  each  having  a  clear  opening  of  33  ft.  4  in.  wide. 

Turnouts. — Under  the  term  "turnout"  are  included  structures 
for  diverting  water  from  the  main  canals  and  laterals  to  the  dis- 
tributaries and  farm  ditches.  The  most  common  form  of  turnout,' 
and  one  which  seems  most  satisfactory,  consists  of  a  box  or  pipe 
opening  through  the  bank  of  the  main  canal  and  controlled  on  the 
inner  side  by  a  gate  or  flash  board.  To  provide  for  drawing  a  supply 
from  the  canal  when  it  is  only  partly  filled,  turnouts  should  be  lo- 
cated as  low  as  possible.  On  account  of  the  important  position  they 
occupy,  and  the  difficulties  of  renewing  them,  turnouts  from  main 
canals  should  be  of  permanent  construction.  Where  the  amount  of 
water  to  be  diverted  is  considerable,  a  solid  conduit  of  masonry  or 
concrete  should  be  used  as  shown  in  Fig.  17;  where  only  a  small 
opening  is  required  vitrified  or  cement  pipes  laid  with  tightly 
cemented  joints  are  satisfactory  as  shown  in  Fig.  18. 

In  the  placing  of  the  turnout,  cut-off  walls  should  be  constructed 
around  the  conduit  or  pipe  and  the  earth  filling  around  them  should . 
be  carefully  tamped  or  puddled  in  order  to  prevent  seepage  and  a 
possible  washing  out  of  the  structure.  Where 'very  large  openings 
are  required,  as,  for  example,  at  the  diversion  to  a  large  lateral, 
masonry  or  concrete  sluices,  controlled  by  gates,  are  constructed 
through  the  banks.  The  upper  and  lower  ends  of  turnouts  should 
be  protected  by  means  of  ample  wing  walls  or  heavy  water-tight 
paving  on  the  slopes  to  prevent  erosion  and  seepage.  Each  turnout 
should  be  provided  with  a  means  of  controlling  the  flow,  so  arranged 
that  it  can  be  easily  operated,  and  securely  fastened  in  position. 

On  the  older  canals  most  of  the  turnouts  as  well  as  other  structures 


68        PRINCIPLES  OF  IRRIGATION  ENGINEERING 

were  built  originally  of  wood.     A  drawing  of  the  details  of  one  of 
the  ordinary  wooden  boxes  is  shown  in  Fig.  19. 

Where  the  head  on  a  turnout  is  considerable,  say  above  3  ft.,  it 


should  in  general  be  controlled  by  means  of  gates.  For  low  heads, 
flash  boards  may  be  used.  They  are,  however,  more  or  less  unsatis- 
factory in  important  structures  on  account  of  the  difficulty  of  regu- 
lating the  flow  and  the  tendency  to  constant  leakage. 


CANAL  STRUCTURES 


69 


70        PRINCIPLES  OF  IRRIGATION  ENGINEERING 


The  capacity  of  a  turnout  will  depend  upon  the  capacity  of  the 
canal  which  it  serves.  It  should  be  designed  to  furnish  the  required 
amount  of  water  with  the  minimum  head  in  the  main  canal  at  which 


it  is  to  be  operated.  When  the  pipe  or  conduit  is  short,  so  that  its 
friction  may  be  neglected,  the  velocity  of  flow  through  it  may  be 
computed  from  the  formula  V  =  C\/^gh.  Where  h  equals  the  head 
in  feet,  g  the  force  of  gravity  and  C  a  constant  depending  upon  the 
shape  of  the  orifice,  but  having  an  average  value  of  about  0.8. 


CANAL  STRUCTURES  71 

Checks  and  Drops. — Checks  and  drops  are  used  to  regulate  the 
surface  elevation  and  velocity  of  flow  in  canals. 

The  term  "check"  is  commonly  applied  to  a  structure  which  closes 
a  part  of  the  waterway  of  a  canal  and  holds  the  water  on  its  upstream 
side  at  a  greater  elevation  than  on  its  downstream  side.  Checks  are 
sometimes  built  in  the  form  of  long-crested  overflow  weirs  extending 
across  the  canal  and  sometimes  in  the  form  of  a  structure  carried  well 
up  above  the  water  surface  and  having  an  opening  or  openings 
through  which  the  water  discharges.  In  each  of  these  forms  there 
is  a  drop  in  the  water  surface  in  passing  it.  The  chief  purpose  of  a 
check  in  a  canal  is  to  hold  up  the  water  surface  at  delivery  points 
while  the  canal  is  being  operated  at  part  capacity.  This  permits 
water  being  delivered  to  lands  which,  in  some  cases,  could  not  other- 
wise be  reached  except  with  the  canal  running  full.  Checks  are  also 
sometimes  used  to  reduce  grades  and  thereby  lessen  the  velocities  in 
canals. 

The  term  "drop"  is  applied  to  a  structure  through  which  water 
is  transferred  from  a  higher  to  a  lower  elevation.  Drops  are  used 
where  the  slope  of  the  country  over  which  a  canal  passes  is  greatej 
than  the  allowable  slope  of  the  canal,  the  real  purpose  of  the  drops 
being  to  reduce  the  effective  grade  or  slope  in  the  canal,  and  thereby 
lessen  its  velocity  by  using  up  a  portion  of  the  grade  in  vertical  or 
nearly  vertical  falls. 

The  accompanying  Fig.  22  gives  the  principal  dimensions  of  the 
ordinary  drop  built  of  timber  such  as  has  been  employed  on  the 
older  canals.  On  the  larger  systems  now  being  built  throughout 
the  West  these  are  replaced  by  concrete  structures  such  as  is 
illustrated  in  Fig.  23. 

Drops  are  commonly  of  two  general  types,  classed  as  vertical  or 
inclined.  In  a  vertical  drop  the  water  is  allowed  to  fall  freely,  while 
in  an  inclined  drop  it  is  carried  down  an  incline  by  means  of  a  chute 
or  some  form  of  channel  built  of  material  not  easily  eroded.  Water 
in  passing  a  drop  acquires  velocity  which  must  be  destroyed  before 
it  enters  the  cha,nnel  below,  in  order  to  prevent  erosion.  The  most 
common  method  of  destroying  this  velocity  is  to  allow  the  moving 
stream  to  fall  into  a  pool  of  water  at  the  foot  of -the  drop.  The 
pool  in  this  case  forms  a  water  cushion  which  absorbs  the  energy  of 
the  falling  water.  Water  cushions  may  receive  the  stream  either 
vertical  or  at  an  angle  inclined  to  the  vertical.  In  the  latter  case 
the  impingement  of  the  stream  into  the  water  below  causes  currents 


72        PRINCIPLES  OF  IRRIGATION  ENGINEERING 


CANAL  STRUCTURES 


73 


which  tend  to  serious  erosion  in  the  sides  of  the  channel  near  the 
foot  of  the  structure.     (See  Plate  VI,  Figs.  A  and  B.) 


2  Planks 

Half  Section  B-B 


Section  C-C 


FIG.  22. — Type  of  timber  drop  for  small  canals. 

In  vertical  drops  there  is  a  less  tendency  to  erosion  in  the  sides  of 
the  channel.     Since,  on  account  of  the  absence  of  the  horizontal 


74        PRINCIPLES  OF  IRRIGATION  ENGINEERING 

component  in  the  velocity,  fewer  currents  are  set  up.  There  is  a 
tendency,  however,  in  vertical  drops  for  erosion  to  take  place  in  the 
bottom  of  the  channel,  where  the  stream  impinges.  The  remedy 
against  erosion  in  either  case  is  to  provide  sufficient  width  and  depth 


V«ntPlpei;lJ$  out  from 
and  8  below  Lip  of  Drop 


Section  A  -A 


FIG.  23. — Type  of  concrete  drop. 

of  water  cushion  to  receive  and  absorb  the  shock  of  the  falling  water 
without  allowing  it  to  impinge  on  the  walls  or  bottom  of  the  cushion 
with  sufficient  force  to  injure  them.  Where  a  water  cushion  is  to 
receive  any  considerable  velocity  it  should  be  built  of  masonry  or 
other  permanent  material. 


CANAL  STRUCTURES  75 

The  size  and  depth  of  water  cushion  required  for  a  given  head  and 
quantity  of  flow  are  questions  upon  which  engineers  are  somewhat 
at  variance,  and  experimental  data  for  determining  the  proper 
relations  of  these  quantities  is  lacking.  Some  observations  made  in 
India  show  that  where  the  ratio  of  height  of  fall  to  depth  of  water 
cushion  is  as  3  to  4,  the  flow  had  no  injurious  effects  on  the  bottom 
of  the  pool.  So  far  as  known,  however,  no  careful  set  of  observations 
showing  the  relations  between  height  of  fall,  quantity  of  discharge 
and  depth  to  which  the  effect  of  the  stream  is  appreciable,  have  ever 
been  made. 

In  practice,  water  cushions  are  usually  constructed  with  a  depth 
of  about  one-third  that  of  the  maximum  fall,  that  is,  one-third  of 
the  height  of  weir  above  the  surface  of  water  below  it,  plus  the 
maximum  depth  of  water  flowing  over  the  weir.  It  is  believed 
that  for  drops  where  the  height  of  fall  is  not  great  this  depth  of 
cushion  is  sufficient.  The  length  of  cushion  required  will  depend 
somewhat  upon  the  height  of  fall  and  quantity  of  water  discharged. 
It  should  be  sufficient  to  permit  the  water  to  come  to  a  nearly  quies- 
cent state  before  it  reaches  the  ordinary  section  of  the  canal  below. 
The  minimum  length  of  cushion  should  not  be  less  than  three  or 
four  times  its  depth.  The  width  of  a  cushion  should  be  somewhat 
greater  than  the  length  of  the  overflow  weir.  One  of  these  inclined 
drops  or  reinforced  concrete  chute  designed  to  take  the  place  of 
ordinary  drop  on  a  steep  grade  is  shown  in  Fig.  24  with  water 
cushion  at  the  bottom. 

With  inclined  drops  of  considerable  height,  a  type  of  channel  is 
sometimes  used  which  offers  a  large  amount  of  resistance  to  the  flow 
of  the  water  and  prevents  it  acquiring  a  high  velocity  in  its  descent. 
These  channels  are  sometimes  constructed  of  rough  stones  so  placed 
as  to  offer  the  maximum  resistance  to  flow.  In  addition  to  the  rough 
walls  and  bottom,  rock  barriers  projecting  above  the  water  surface 
are  placed  at  frequent  intervals  in  the  channel.  Another  and  very 
effective  method  of  reducing  velocity  in  an  inclined  drop  is  to  con- 
struct it  in  the  form  of  a  series  of  vertical  drops  with  a  water  cushion 
at  the  foot  of  each.  By  such  a  device  the  velocity  is  killed  at  each 
water  cushion  and  the  maximum  velocity  which  will  be  acquired  will 
depend  upon  the  height  of  the  secondary  drops. 

In  the  design  and  construction  of  drops  for  a  canal  over  country 
where  the  slope  is  considerable,  it  is  necessary  to  do  a  large  amount  of 
preliminary  work  in  order  to  reach  the  most  economical  solution. 
The  principal  points  to  be  considered  in  this  connection  are  the 


76       PRINCIPLES  OF  IRRIGATION  ENGINEERING 


CANAL  STRUCTURES  77 

relative  costs  of  a  canal  with  fewer  drops  of  greater  height,  compared 
to  one  with  more  drops  of  lesser  height.  In  the  former  case  it  must 
be  taken  into  account  also  that  more  excavation  will  be  required  on 
account  of  the  increased  depth  of  the  canal  below  the  high  drops. 
In  some  cases  where  the  slope  of  the  country  is  very  great  it  is  more 
economical  to  line  a  canal  with  masonry  so  that  it  will  stand  high 
velocities,  than  to  construct  the  necessary  drops  to  reduce  its  veloc- 
ity to  a  maximum  for  an  earth  canal.  The  latter  method  is  in 
effect  the  construction  of  a  long  inclined  drop.  No  general  state- 
ments can  be  made  relative  to  the  most  economic  method  of  handling 
special  cases,  each  must  be  considered  in  the  light  of  all  factors  which 
affect  its  efficiency  and  cost  in  order  to  reach  a  satisfactory  solution. 
(See  Plate  VI,  Fig.  C.) 

Checks  and  drops  are  frequently  combined  in  one  structure, 
which  is,  in  fact,  simply  providing  a  means  for  holding  up  the  water 
in  the  canal  above  the  drop.  This  may  be  done  by  a  flash  board  or 
gate  regulation,  the  size  of  opening  being  adjusted  to  hold  the  water 
up  to  the  required  height.  The  up-stream  side  of  a  drop  is  some- 
times constructed  as  a  weir  with  its  crest  raised  some  distance  above 
the  grade  of  the  canal.  This  weir  automatically  acts  as  a  check  for 
holding  the  water  up  in  the  canal  but  has  the  disadvantages  of 
increasing  the  height  of  drop  for  low  discharges  and  not  permitting 
the  canal  to  drain  completely.  All  drops  of  this  kind  should  have  a 
small  drain  to  completely  unwater  the  canal.  Immediately  above 
a  drop  which  is  given  a  free  discharge  there  is  a  rapid  drawing  down 
of  the  water  in  the  canal  and  a  corresponding  increase  in  the  velocity 
of  the  flow.  These  high  velocities  have  a  tendency  to  destroy  the 
canal  above  a  drop  and  if  for  no  other  reason  than  that  of  protection 
it  is  ordinarily  necessary  to  regulate  the  flow  over  a  drop  so  that  the 
water  above  will  not  be  drawn  down  to  any  appreciable  extent. 
One  method  of  doing  this  is  by  means  of  the  notched  drop. 

This  notched  drop  (Fig.  25)  is  used  extensively  in  India  and 
has  been  introduced  in  the  United  States.  In  this  form  of  drop 
the  canal  discharges  from  the  upper  channel  into  the  pool  below 
through  one  or  more  notches  of  such  size  and  shape  that  the  amount 
of  flow  through  them  for  any  given  depth  is  very  nearly  equal  in 
amount  to  that  carried  by  the  canal  with  the  same  depth.  A  notch 
which  for  all  depths  will  theoretically  discharge  the  same  quantity 
of  water  as  will  be  carried  by  a  trapezoidal  canal  section  has  curved 
sides  and  bottom.  Practically,  however,  this  refinement  is  unneces- 
sary, and  a  notch  may  be  made  with  straight  sides  and  bottom 


78        PRINCIPLES  OF  IRRIGATION  ENGINEERING 


CANAL  STRUCTURES  79 

which  will  fulfill  practical  requirements.  The  exact  shape  and 
size  of  notch,  that  is  the  width  of  bottom  and  slope  of  the  sides, 
which  is  required,  will  depend  upon  the  size  and  section  of  the 
canal  and  must  be  designed  for  each  particular  case.  With  drops 
of  any  considerable  size  it  is  preferable  to  use  several  notches 
instead  of  one.  This  permits  the  water  being  broken  up  and  dis- 
tributed more  nearly  over  the  entire  surface  of  the  cushion  below 
and  reduces  its  cutting  effect.  If  a  semi-circular  lip  be  projected 
for  a  short  distance  down-stream  from  the  foot  of  each  notch  the 
water  can  be  further  spread  out  and  its  erosive  effect  still  further 
diminished.  (See  Plate  VI,  Fig.  B.) 

Wasteways. — The  term  "wasteway"  applied  to  canals,  includes 
two  distinct  classes  of  structures.  The  first,  which  is  commonly 
called  an  overflow  spillway,  is  used  to  discharge  the  waters  from  a 
canal  when  it  becomes  filled  above  its  normal  capacity.  Such  a 
spillway  is  automatic  in  its  action  and  serves  as  a  safety  valve  to 
prevent  a  canal  being  overloaded  and  its  banks  topped  and  washed 
away.  The  second  class  of  structures  commonly  known  as  a  sluice 
gate,  is  used  for  emptying  a  canal.  Sluice  gates  in  general  are  not 
automatic  in  their  action,  but  are  ordinarily  provided  with  the  neces- 
sary means  for  opening  them  quickly.  They  serve  as  a  means 
for  rapidly  drawing  down  the  water  in  a  canal  in  case  of  an  emergency, 
such  as  a  break,  or  when  repairs  are  necessary. 

Overflow  spillways  and  sluice  gates  are  both  to  a  large  degree 
protective  in  their  nature;  the  first  providing  a  safeguard  against 
accident,  and  the  second  a  means  for  reducing  the  damage  should 
an  accident  occur.  It  cannot  be  said  that  the  use  of  either  is 
absolutely  necessary  at  a  particular  place  in  a  canal,  but  experience 
has  shown  that  the  protection  which  they  afford  to  an  important 
canal  is  well  worth  their  cost. 

The  requirements  for  location  for  the  two  classes  of  structures 
do  not  differ  greatly.  In  one  important  respect,  that  of  requiring 
a  wasteway  channel,  they  are  similar.  In  other  words,  in  the 
location  of  either  a  spillway  or  sluice  gate  a  site  must  be  selected 
from  which  it  is  possible  to  carry  the  waste  water  without  undue 
damage  to  the  adjacent  lands.  On  this  account  it  is  sometimes 
feasible  and  economical  to  construct  both  a  spillway  and  sluice 
gates  at  the  same  point  on  a  canal.  The  location  of  these  structures 
should  be  such  that  they  are  accessible  and  provide  for  the  greatest 
degree  of  efficiency.  In  general  they  should  be  located  at  or  near 
the  lower  end  of  that  stretch  of  the  canal  they  are  intended  to 


80        PRINCIPLES  OF  IRRIGATION  ENGINEERING 

protect,  since  at  this  point  the  protection  from  overflow  and  the 
drainage  of  a  canal  can  be  most  easily  effected.  The  frequency 
at  which  the  structures  should  be  located  is  dependent  upon  the 
size  and  importance  of  the  canal. 

In  the  design  of  an  overflow  spillway  there  must  be  considered 
first  the  maximum  quantity  of  water  it  shall  discharge,  and  second, 
the  maximum  rise  above  the  normal  elevation  of  water  surface 
which  the  canal  will  stand.  These  factors  are  both  uncertain  and 
may  in  some  cases  be  classed  as  mere  assumptions.  In  general  it 
may  be  assumed,  however,  that  the  maximum  capacity  of  an  over- 
flow spillway  need  not  exceed  50  per  cent,  of  the  capacity  of  a  canal, 
and  that  the  maximum  rise  of  water  in  the  canal  should  not  exceed 
from  30  to  50  per  cent,  of  the  minimum  free  board. 

Having  established  the  discharge  and  head  of  water  available, 
the  length  of  spillway  required  may  be  computed  from  the  weir 
formulae  by  selecting  the  proper  coefficient  for  the  particular  form 
of  weir  crest  to  be  used.  The  form  of  weir  crest  and  channel  to  be 
used  will  depend  to  a  great  extent  upon  the  topography  of  the  site 
and  the  character  of  the  material.  Spillways  should  as  a  rule  be 
located  where  the  canal  is  well  in  cut  in  order  to  r  rovide  safe  founda- 
tion for  the  overflow  weir  and  waterway  leading  from  the  weir  over 
the  banks.  This  waterway  should  be  water  tight  and  for  safety 
should  be  of  permanent  masonry  construction. 

For  collecting  the  discharge  from  a  long  weir  and  concentrating 
it  in  a  channel  of  small  width  various  methods  have  been  used.  One 
is  to  construct  the  upper  portion  of  the  outlet  channel  parallel 
to  the  weir  crest  and  discharge  into  it  laterally.  Another  method 
is  to  concentrate  the  length  of  overflow  weir  rjy  constructing  it  in  a 
dentated  form,  thus  reducing  the  total  width  pf  spillway  opening. 

A  sluiceway  for  the  protection  of  a  canal  should  in  general  have 
a  capacity  not  less  than  that  of  the  canal  so  that  if  necessary  the 
entire  flow  may  be  diverted.  The  bottom  of  a  sluice  gate  should  be 
some  distance  below  the  grade  of  a  canal,  in  order  to  increase 
its  capacity  and  make  it  more  effective  in  its  operation.  The 
gates  closing  a  sluiceway  should  be  of  a  type  easily  operated 
and  fitted  with  the  necessary  devices  to  insure  their  operation  when 
required. 

Culverts. — In  connection  with  canal  construction,  culverts  are 
used:  first  to  carry  drainage  water  under  the  canals,  and,  second,  to 
carry  canals  under  roadways  or  through  embankments  where  open 
cuts  are  not  feasible.  Whether  a  culvert  be  used  for  carrying  water 


PLATE  VI 


FIG.  A. — Series  of  checks  and  drops  with  inclined  chutes  terminating  in  water 
cushion  with  concrete  blocks  to  break  the  force  of  the  water.  North  Platte 
Project,  Nebr. 


j>'     "ft** 


FIG.  B. — Notched  check  and  drop  with  projecting  lip  beneath  each  notch  to  dif- 
fuse and  break  the  force  of  the  falling  water.     Rio  Grande  Project,  N.  Mex. 

(Facing  Page  80) 


PLATE  VI 


FIG.  C. — Concrete  chute,  built  instead  of  a  series  of  drops,  and  terminating 
in  a  water  cushion  with  concrete  baffle  board.     Boise  Project,  Idaho. 


FIG.  D. —  Spillway  lip  to  automatically  permit  escape  of  excess  water  from 
canal  back  into  river  and  sluice  gates  provided  to  facilitate  scouring  out  of 
materials  deposited  in  upper  portion  of  canal.  Salt  River  Project,  An'/. 


CANAL  STRUCTURES  81 

under  a  canal  or  whether  it  be  used  for  carrying  the  waters  of  the 
canal,  the  general  principles  of  its  construction  do  not  differ  mate- 
rially. The  principal  points  to  be  considered  in  the  design  and  con- 
struction of  culverts  are  size  or  capacity,  section,  grades,  economy 
and  permanency  of  construction. 

The  capacity  of  a  culvert  to  carry  the  waters  of  a  canal  will  be 
limited  to  the  capacity  of  the  canal.  The  capacity  of  a  culvert  to 
carry  drainage  water  under  a  canal  was  treated  under  Lateral  Drain- 
age. In  this  connection,  attention  is  called  to  the  fact  that  errors  in 
the  capacity  of  drainage  culverts  are  likely  to  be  on  the  side  of  mak- 
ing them  too  small  rather  than  too  large.  It  is  impossible  to  prove 
that  a  culvert  is  too  large  but  a  very  simple  matter  to  prove  that  it  is 
too  small  should  its  capacity  once  be  overtaxed.  The  section  of  a 
culvert  carrying  an  irrigation  canal  is  important  on  account  of  the 
grade  it  may  require.  In  order  that  no  extra  grade  be  consumed  by 
the  passage  of  water  through  a  culvert  its  cross-section,  both  as 
regards  shape  and  area,  must  be  practically  the  same  as  that  of  the 
canal.  If  the  area  of  the  waterway  be  contracted  so  that  a  higher 
velocity  is  required  in  the  culvert  than  in  the  canal,  additional  grade 
is  necessary  to  produce  and  maintain  the  added  velocity.  If  the 
shape  of  the  waterway  is  changed  additional  friction  results,  which 
also  requires  head  to  overcome. 

On  account  of  the  excessive  cost,  it  is  not  practical  in  most  cases, 
to  construct  culverts  of  the  same  shape  and  area  of  cross-section  as 
the  canal  of  which  they  form  a  part.  In  most  cases,  economy  can  be 
effected  both  by  reducing  the  area  of  the  cross-section  and  by  building 
it  of  such  a  shape  that  the  minimum  amount  of  material  is  required  for 
the  maximum  cross-sectional  area.  The  most  economic  section,  so 
far  as  hydraulic  properties  and  amount  of  material  required  are  con- 
cerned, is  the  circle.  This  section  is  not  always  practical,  however, 
on  account  of  the  abrupt  changes  which  it  introduces  in  the  channel. 
For  example,  a  canal  2.5.  ft.  deep  and  having  an  average  width  of 
20  ft.  will  have  practically  the  same  cross-sectional  area  as  a  circular 
culvert  whose  diameter  is  7.3  ft.  On  account  of  the  necessity  of 
contracting  the  stream  and  the  lowering  of  the  grade  of  the  culvert 
far  below  that  of  the  canal  a  round  culvert  is  not  the  most  favorable 
for  wide  and  shallow  canals. 

Where  a  culvert  is  intended  to  carry  drainage  water  different  con- 
ditions ordinarily  prevail,  and  the  same  necessity  for  conforming  the 
shape  of  the  culvert  to  the  shape  of  the  canal  does  not  exist.  In 
general,  however,  the  grade  of  a  culvert  should  not  be  much  below 


82        PRINCIPLES  OF  IRRIGATION  ENGINEERING 

the  grade  of  the  waterway  in  order  to  avoid  its  being  silted  partly 
full  and  rendered  less  effective  when  it  is  needed. 

The  forms  of  culverts  most  generally  in  use  are  what  are  commonly 
designated  as  "barrel"  and  "box"  culverts,  the  former  being  ordi- 
narily a  circle  or  ellipse  and  the  latter  of  rectangular  form.  According 
to  the  materials  used,  culverts  may  be  classified  as  wood,  pipe,  and 
masonry.  Wood  culverts  are  commonly  constructed  in  rectangular 
form  and  consist  of  a  framework  sufficiently  strong  to  carry  the  em- 
bankment above,  covered  with  planking  which  forms  the  waterway. 


Note :  The  channel  above  and  below  the  culvert  should  be  pretested  with  grouted  rlp-rap 
or  pavfau?  to  the  distance  required  bj  local  conditions. 


FIG.  26. — Vitrified  pipe  culvert  with  concrete  inlet  and  outlet. 

Pipe  culverts  (Fig.  26)  are  either  vitrified,  concrete,  iron  or  steel. 
Masonry  culverts  are  generally  constructed  of  either  stone  or 
concrete. 

The  selection  of  the  materials  from  which  a  culvert  is  to  be  made 
involves  questions  of  cost,  importance,  and  durability  of  the  structure. 
In  most  sections  of  the  country  culverts  can  be  constructed  of  wood 
at  a  less  cost  than  from  other  materials.  On  account  of  the  perish- 
able nature  of  wood,  however,  it  is  not  satisfactory  for  permanent 
work.  For  small  openings,  not  exceeding  say  4  or  5  ft.  in  diameter, 
pipe  culverts  are  satisfactory.  Whether  or  not  vitrified,  concrete, 
iron  or  steel  pipe  be  used  will  depend,  to  a  certain  extent,  upon  the 
relative  cost  of  these  materials  in  the  particular  locality  where  they 
are  to  be  used.  Vitrified,  or  concrete  pipe,  with  joints  laid  in  ce- 
ment mortar,  make  a  very  satisfactory  culvert. 

For  large  openings,  say  those  exceeding  5  or  6  ft.  in  diameter, 
culverts  should,  in  most  cases,  be  constructed  of  solid  masonry, 
either  stone  or  concrete.  During  the  last  few  years,  or  since  1905, 
satisfactory  structures  of  this  kind  have  been  made  of  reinforced 


CAXAL  STRUCTURES 


83 


concrete,  the  reinforcement  permitting  the  reduction  of  the  thickness 
of  the  walls  and  greatly  reducing  the  quantity  of  concrete  required 
and  corresponding  cost  of  the  structure  (Fig.  27). 

In  the  design  of  all  culverts,  especial  care  must  be  exercised  to  see 
that  they  are  of  sufficient  strength  to  carry  the  weight  imposed  upon 
them  by  the  embankment  above.  Another  essential,  especially  in 
culverts  under  canals  or  waterways,  is  that  they  shall  be  water-tight. 
Seepage  along  culverts  should  be  guarded  against  by  the  construction 
of  ample  cut-off  or  curtain  walls.  Where  a  culvert  is  designed  to  be 
operated  under  a  head,  these  cut-off  walls  should  be  carried  entirely 


Deration  of  Upper  Portal 


Elevation  of  Lower  Portal 


FIG.  27. — Reinforced  concrete  culvert. 

around  the  culvert.  Approaches  to  culverts  should  be  protected 
by  wing  and  curtain  walls  and  the  bottom  and  sides  of  the  channel 
should  be  paved.  Where  there  is  a  material  change  in  the  shape  of 
the  cross-section  from  a  canal  to  a  culvert  such  change  should  be  made 
gradual  in  order  to  reduce,  so  far  as  possible,  the  amount  of  friction 
and  entry  head  required. 

Flumes. — Where  topographic  conditions  are  such  as  to  make  ordi- 
nary canal  construction  impracticable,  flumes  are  frequently  used. 
In  general,  flumes  may  be  classified  as  bench  and  trestle  flumes. 

Bench  flumes  are  used  on  side  hill  work  where  the  slopes  are  too 
steep  or  the  material  unsuitable  for  an  open  canal.  The  foundation 
for  such  a  flume  is  excavated  in  the  side  of  the  slope  and  should 


84        PRINCIPLES  OF  IRRIGATION  ENGINEERING 

be  level  transversely  and  have  approximately  the  same  grade  as  the 
flume  horizontally.  The  important  points  to  be  considered  in  pre- 
paring the  foundation  to  receive  the  flume  are  :  (a)  Security  against 
unequal  settlement  in  the  foundation;  and  (b)  security  against 
injury  to  the  flume  by  slides  of  rock  or  earth. 

Bench  or  side  hill  flumes  should  be  supported  upon  natural  mater- 
ials when  practicable,  the  excavation  being  made  somewhat  wider 
than  the  flume.  Where,  on  account  of  the  excess  cost  of  excava- 
tion, as  is  sometimes  the  case  on  steep,  rocky  slopes,  it  is  uneconom- 
ical to  excavate  into  the  slope  wide  enough  to  receive  the  flume,  the 
lower  edge  of  the  bench  should  be  built  up  of  rock  or  masonry  to 
make  it  secure  against  settlement.  As  a  general  rule,  flumes  should 
not  be  supported  upon  an  earthen  foundation  part  in  cut  and  part 
in  embankment,  as  the  embankment  portion  is  almost  sure  to  settle. 
Foundations  for  bench  flumes,  especially  if  they  be  of  earth,  should 
be  carefully  drained  to  care  for  seepage  and  storm  water  carried 
down  over  the  slopes.  The  drainage  water  should  be  collected  along 
the  upper  edge  of  the  bench  and  carried  across  it  at  frequent  intervals 
in  well-protected  channels.  Where  large  waterways  are  crossed  on 
the  slope  the  flume  should  be  carried  over  them  by  means  of  trestles 
or  suitable  spans  in  order  to  leave  ample  waterways  below. 

The  excavated  slopes  above  the  bench  should,  for  the  sake  of 
economy,  be  made  as  steep  as  they  will  safely  stand.  The  degree 
of  steepness  will  depend  partly  upon  the  character  of  the  materials 
and  partly  upon  climatic  conditions.  Especial  care  should  be 
exercised  to  see  that  all  masses  of  rock  which  are  partly  loose  are 
removed.  In  choosing  the  location  for  a  side  hill  flume  care  must  be 
exercised  to  see  that  the  location  is  a  sufficiently  safe  one  that,  with 
reasonable  care  and  attention,  the  flume  can  be  continuously  main- 
tained and  operated. 

Trestle  flumes  are  used  for  carrying  canals  across  depressions. 
One  of  the  principal  questions  to  be  determined  in  connection  with 
their  use  is  that  of  feasibility.  This  should  be  determined  by  care- 
fully prepared  estimates  of  the  various  plans  by  which  the  work  can 
be  accomplished.  In  making  such  estimates  weight  must  be  given 
to  permanency  and  cost  of  future  maintenance,  as  well  as  to  initial 
cost.  For  example,  a  canal  constructed  in  an  embankment  of  suit- 
able material,  even  though  its  first  cost  exceed  that  of  a  flume,  might 
eventually  be  far  cheaper  on  account  of  its  permanent  character  and 
low  cost  of  maintenance. 

Conditions  are  occasionally  so  much  in  favor  of  a  particular  kind 


CANAL  STRUCTURES 


85 


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86        PRINCIPLES  OF  IRRIGATION  ENGINEERING 

of  construction  that  comparative  estimates  are  hardly  necessary, 
while  in  other  cases  careful  and  detailed  estimates  are  required. 
Where  first  costs  do  not  differ  materially,  preference  should  be  given 
to  the  plan  which  is  most  permanent  in  character  and  requires  the 
least  expenditure  for  maintenance.  It  is  often  necessary  to  consider 
also  the  amount  of  water  losses.  For  a  tight  flume  the  losses  by 
seepage  and  evaporation  evidently  will  be  less  than  from  an  earthen 
canal  constructed  of  more  or  less  porous  material.  For  this  reason, 
flumes  are  sometimes  used  to  reduce  seepage  and  evaporation  losses. 

In  constructing  a  trestle  flume,  the  foundation  is  of  prime  impor- 
tance. If  a  trestle  be  of  wood  (Fig.  28)  or  other  perishable  material, 
it  should  be  placed  upon  masonry  carried  well  up  above  the  surface 
of  the  ground.  On  account  of  the  possibility  of  the  ground  under  a 
flume  becoming  saturated,  excessive  loadings  may  cause  settlement 
and  should  be  avoided.  Where  possible,  drainage  for  foundations 
should  also  be  provided.  In  high  trestles,  wind  pressure  should  be 
considered  and  the  structure  made  safe  against  overturning  from 
this  cause. 

The  materials  in  the  United  States  available  for  flume  construction 
and  within  reasonable  limits  of  cost  are  wood,  metal,  and  concrete. 
Wooden  flumes  can  be  built  for  the  lowest  first  cost  in  many  sections 
of  the  arid  west  where  timber  is  comparatively  cheap.  On  account 
of  the  perishable  nature  of  wood,  however,  the  life  of  a  flume  of  this 
character  is  short  and  maintenance  charges,  especially  after  the 
first  few  years,  correspondingly  high.  Flumes  are  usually  wet  only 
a  portion  of  the  year  and  the  alternate  action  of  water  and  sun  upon 
lumber  has  a  tendency  to  warp  and  crack  it,  so  that  it  is  difficult  to 
maintain  a  wooden  flume  in  a  water-tight  condition.  For  the  above 
reasons  wooden  flumes  are  not  entirely  satisfactory  and  their  con- 
struction should  be  avoided  if  possible. 

A  type  of  flume  used  quite  largely  and  one  which  has  given  satis- 
faction is  a  metal  waterway  supported  upon  a  trestle  or  foundation 
of  wood.  These  metal  flumes  are  now  manufactured  from  plates  of 
comparatively  pure  iron,  which  it  is  claimed  is  less  affected  by  corro- 
sion than  ordinary  iron  or  steel.  The  accompanying  Fig.  29  gives 
the  principal  dimensions  of  one  of  these  metal  flumes,  supported 
on  wooden  trestles  and  provided  at  the  ends  with  concrete  inlet 
and  outlet.  A  view  of  such  flume  in  use  is  shown  in  Plate  VII, 
Fig.  D. 

Reinforced  concrete  flumes  have  been  constructed  in  some  local- 
ities. On  account  of  the  lasting  qualities  of  this  material  it  is  prob- 


CANAL  STRUCTURES 


87 


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88        PRINCIPLES  OF  IRRIGATION  ENGINEERING 

able  that  the  life  of  such  a  flume  will  be  many  times  that  of  one  built 
from  wood  or  metal.  The  first  cost  of  concrete  flumes  is  relatively 
high  but  their  superior  lasting  qualities  and  low  maintenance  costs 
seem  to  entitle  them  to  consideration  from  an  economic  standpoint. 
(See  Plate  VII,  Fig.  A.) 

In  wood  and  metal  flumes  the  waterway  or  lining  should  be  so  con- 
structed that  it  can  be  replaced  without  disturbing  the  main  struct- 
ure. This  permits  of  repairs  being  readily  made  to  the  lining  which 
ordinarily  fails  first.  Various  plans  have  been  tried  with  more  or 
less  success  for  making  the  joints  of  wooden  flumes  water  tight.  The 
most  common  form  of  joints  are  caulked,  battened  and  loose  splined. 
Of  these  it  is  believed  that  splines  are  the  most  satisfactory  in  pro- 
ducing a  joint  secure  against  leaks.  In  a  joint  of  this  kind  the 
thickness  of  the  spline  should  be  the  same  as  the  width  of  the  groove 
and  the  width  of  spline  slightly  less  than  twice  the  depth  of  the 
groove.  The  latter  precaution  is  necessary  to  prevent  the  spline 
being  split  when  the  planks  of  the  lining  are  driven  together. 

Where  a  flume  joins  an  earthen  embankment  especial  care  must  be 
taken  to  prevent  the  current  cutting  around  its  ends  since  water  has 
a  tendency  to  follow  a  joint  between  earth  and  a  hard  pr  smooth 
material  such  as  wood  or  concrete.  One  of  the  best  methods  of 
preventing  this  erosion  around  the  ends  is  to  enlarge  the  ends  of  the 
flume  for  a  distance  of  15  or  20  ft.  and  carry  the  earthen  embankment 
into  these  enlarged  ends.  That  portion  of  the  flume  into  which  the 
earth  filler  is  carried  should  have  its  floor  depressed  to  a  depth  of 
2  or  3  ft.  below  the  grade  of  the  canal  and  its  side  walls  carried  well 
out  into  the  center  of  the  canal  embankments.  A  curtain  wall 
should  also  be  carried  down  at  the  ends  of  the  flume  (see  Fig.  29). 
The  bottom  and  slopes  of  the  canal  for  some  distance  from  the  ends 
of  a  flume  should  be  protected  by  means  of  rock  or  other  form  of 
paving.  This  paving,  if  constructed  with  rough  surface,  tends  to 
check  the  velocity  of  flow  along  the  sides  and  bottom  of  the  canal 
and  reduces  the  chances  of  erosion. 

Velocity  and  Flow  of  Water  in  Flumes. — In  order  to  reduce  the 
size  of  a  flume  to  a  minimum,  the  velocity  of  flow  in  it  should  exceed 
that  in  the  canal.  Flumes  are  generally  of  material  that  will  stand 
high  velocities  without  danger  of  erosion;  the  velocities  which  may 
be  attained  in  them  are  usually,  however,  limited  by  the  grades 
available  and  the  checking  of  the  flow  at  the  lower  end  of  the  flume 
rather  than  by  the  velocity  which  the  material  will  stand. 

The  velocity  of  flow  in  a  flume  may  be  computed  from  the  slope, 


PLATE  VII 


^^^^••^^^^•^•••™  ^••-— •  

FIG.  A. — Concrete  flume  carrying  water  of  main  canal  across  side  drainage  lines. 
North  Platte  Project,  Wyo.-Nebr. 


FIG.   B. — Concrete  inverted  siphon    carrying  water  of  main  canal  under  side 
drainage  line  instead  of  over  it.     North  Platte  Project,  Wyo.-Nebr. 

(Facing  Page  88) 


:je***y 
<<£>^W 


FIG.  C. — Concrete  pressure  pipe  used  in  place  of  flume.     Sun  River 
Project,  Mont. 


FIG.  D. — Metal  flume  on  timber  trestle. 


CANAL  STRUCTURES  89 

hydraulic  mean  radius,  and  an  assumed  value  of  "w, "  the  same  as 
for  open  canals.  Where  the  velocity  in  a  flume  exceeds  that  in  the 
canal  above  there  must  be  sufficient  drop  at  the  upper  end  of  the 
flume  to  provide  for  entry  and  increased  velocity  heads.  The 
value  of  the  entry  head  will  depend  upon  the  form  of  transition 
curves  from  the  canal  to  the  flume  section  and  may  ordinarily  in 
practice  be  made  so  small  as  to  be  negligible.  The  increased  velocity 
head  is  the  head  corresponding  to  the  velocity  in  the  flume,  less 
the  head  corresponding  to  the  velocity  in  the  canal  above.  Calling 

Fi2  —  F22 
its  value  h  it  may  be  obtained  from  the  expression  h  =  — 

where  V\  equals  velocity  of  flow  in  the  flume,  Vz  equals  velocity  in 
the  canal  above  and  g  equals  the  acceleration  of  gravity  in  feet  per 
second.  At  the  lower  end  of  a  flume,  where  the  velocity  is  reduced 
to  that  of  the  canal,  there  is  a  slight  gain  in  head  due  to  the  water 
giving  up  a  part  of  its  kinetic  energy.  Theoretically  it  is  possible 
to  regain  the  greater  part  of  this  increased  velocity  head  when  the 
velocity  is  reduced;  practically,  however,  it  is  not  possible  to  regain 
but  a  small  amount  of  it. 

On  account  of  the  resistance  of  change  in  direction,  flumes  intended 
to  carry  water  at  reasonably  high  velocities  should  be  free  from 
sharp  turns  or  reduction  in  grades.  If  these  be  introduced  there 
is  a  tendency  for  the  water  to  pile  up  at  the  point  of  change  and 
possibly  overflow  the  sides  of  the  flume. 

Tunnels. — A  tunnel  in  connection  with  irrigation  works  is  that 
portion  of  a  canal  or  outlet  of  a  reservoir  which  passes  underground 
or  pierces  projecting  ridges.  The  tunnels  on  the  main-line  canals 
are  necessitated  by  the  fact  that,  especially  near  the  heads  of  the 
canals  where  they  leave  the  river,  the  ground  is  frequently  very 
rough  and  open  cuts  are  difficult  if  not  impossible  to  construct  and 
maintain.  Under  these  conditions,  the  most  economical  form  of 
construction  is  to  continue  the  canal  by  suitable  excavations  into 
and  through  the  solid  rock  or  partly  consolidated  earth,  holding 
this  in  place  if  necessary  by  temporary  timbering  to  be  replaced 
later  by  permanent  lining.  In  several  instances  tunnels  of  con- 
siderable length  have  been  built  through  a  mountain  range  or 
plateau  to  bring  water  from  a  distant  river.  The  most  notable  of 
such  tunnels  is  that  on  the  Uncompahgre  Valley  project  in  Colo- 
rado over  30,000  ft.  long  taking  the  entire  summer  flow  of  Gunnison 
River  and  the  tunnel  of  the  Strawberry  Valley  project,  Utah,  over 
22,000  ft.  long,  the  other  dimensions  of  which  are  given  in  Fig.  30. 


90        PRINCIPLES  OF  IRRIGATION  ENGINEERING 


This  takes  the  water  stored  in  Strawberry  Valley  through  the  top 
of  the  Wasatch  range. 

In  planning  tunnels  not  only  should  the  first  cost  be  considered, 
but  more  than  this  the  expense  of  future  maintenance  of  such  tunnel 
as  compared  with  an  open  cut.  The  latter,  especially  on  steep 
hill  sides,  is  exposed  to  many  dangers;  either  it  may  slide  out  as  a 
whole  aided  by  the  weight  of  the  water  and  by  the  softening  of  the 
material,  or  it  may  be  filled,  in  whole  or  part,  by  earth  and  rock 
sliding  in  from  above.  Thus  the  construction  of  a  tunnel  is  often 
justified  even  though  the  first  cost  is  larger  than  that  of  an  open  cut. 

Experience    in    operating    and    maintaining    finished    canals    is 


Portal  Sets 

with 
Transverse  811,1s 


Inside  Sets 

with 
Longitudinal  Sills 


Detail  of  Longitudinal  Sill 

and 
Post  Connection. 


FKJ.  30. — Concrete  lined  tunnel,  Strawberry  Valley  Project,  Utah. 

demonstrating  that  as  a  rule  a  considerable  portion  of  the  canal 
which  has  been  built  in  very  rough  ground  might  have  been  more 
economically  placed  in  tunnel,  because  the  latter  when  once  properly 
constructed  is  relatively  permanent.  The  tendency  is  therefore 
to  construct  canals  more  and  more  in  tunnel  than  in  the  past  and 
in  case  of  doubt  in  poor  locations  to  throw  the  conduit  underground 
rather  than  attempt  to  keep  it  wholly  on  the  surface. 

Tunnels  may  be  built  of  the  full  size  and  capacity  of  the  canal 


CANAL  STRUCTURES  91 

or  for  economy  of  construction,  the  cross-section  may  be  reduced. 
In  the  latter  case,  it  is  obvious  that  the  velocity  through  the  tunnel 
must  be  increased  by  giving  it  additional  grade  and  the  approach 
to  the  tunnel  must  be  so  designed  as  to  provide  sufficient  velocity 
of  entrance  to  permit  water  to  the  entire  capacity  of  the  canal  to 
pass  through  the  tunnel.  This  latter  feature  has  been  neglected 
on  some  notable  works  and  the  tunnels  when  finished  have  been 
found  to  obstruct  the  flow  so  greatly  as  to  necessitate  expensive 
changes. 

The  decrease  of  the  section  of  the  tunnel  and  consequent  increase 
in  slope  results  in  the  canal  descending  somewhat  rapidly  and  thus 
losing  the  advantage  of  elevation  in  commanding  irrigable  land. 
If  the  descent  of  the  ground  from  the  intake  of  the  canal  to  the 
irrigable  land  is  so  great  that  there  is  ample  grade  allowable  without 
sacrificing  irrigable  area,  then  it  follows  that  heavy  grades  can 
be  given  to  the  tunnel  and  corresponding  reduction  of  cross-section. 
But  if,  on  the  other  hand,  the  area  of  irrigable  land  is  limited  by  the 
elevation  to  which  the  water  can  be  delivered,  then  it  may  be 
necessary  to  keep  the  size  of  the  tunnel,  to  the  full  area  of  cross- 
section  of  the  canal  thus  reducing  the  slope  and  keeping  the  canal 
at  the  highest  practicable  elevation.  These  balancing  considerations 
should  be  taken  into  account  in  all  designs  of  canals  where  tunnels 
are  used. 

The  construction  of  tunnels  may  be  considered  as  almost  a 
distinct  branch  of  engineering,  especially  those  in  soft  ground 
where  great  skill  must  be  employed  in  holding  the  roof  and  walls. 
For  the  present  purpose,  it  is  sufficient  to  call  attention  to  the  fact 
that  in  all  tunnel  work  there  necessarily  exist  great  uncertainties 
as  to  the  conditions  to  be  encountered  and  the  probable  time  and 
cost  of  completion.  As  part  of  the  preliminary  survey  and  examina- 
tion, borings  should  be  made  at  short  intervals  along  the  proposed 
route  and  all  possible  facts  obtained  as  guidance  in  preparing  pre- 
liminary estimates  and  plans  and  specifications.  Even  with  the 
most  thorough  exploration  by  drill  holes  and  other  methods  such 
as  are  feasible  under  the  circumstances,  there  are  still  considerable 
risks  to  be  run  and  a  large  contingent  expense  must  be  allowed. 

Lining. — Lining  must  usually  be  provided  for  tunnels  of  this  char- 
acter not  only  to  prevent  the  top  and  sides  from  falling  in  but  also 
to  reduce  the  friction  and  increase  the  capacity  of  the  tunnel  by 
providing  smooth  walls.  It  is  usually  necessary  to  set  timbers  to 
hold  the  roof  and  in  many  instances  it  is  not  safe  to  remove  these 


92        PRINCIPLES  OF  IRRIGATION  ENGINEERING 

timbers;  thus  they  are  left  in  place  being  embedded  in  the  permanent 
concrete  lining.  In  extreme  instances,  it  has  been  found  necessary 
to  use  iron  plates  bolted  together  to  hold  the  soft  materials  from 
falling  into  the  tunnel  and  in  these  cases  also  this  temporary  lining 
is  not  removed  but  is  covered  by  the  concrete. 

Where  the  walls  and  roof  are  of  solid  rock  with  no  apparent  tend- 
ency to  disintegrate  the  tunnel  is  usually  excavated  as  nearly  as 
possible  to  the  prescribed  dimensions  or  neat  lines  and  finished  up 
to  the  true  dimensions  by  a  relatively  thin  lining  of  concrete,  the 
voids  between  the  concrete  and  the  rock  being  filled  with  small  stone. 
For  this  purpose,  forms  of  wood  or  of  metal  are  provided  and  are 
drawn  through  the  tunnel  on  suitable  tracks  or  other  devices,  being 
taken  out  and  advanced  as  rapidly  as  the  concrete  sets. 

Where  the  lining  will  be  subject  to  heavy  pressures  the  thickness 
is  increased  and  all  spaces  filled  in  with  concrete  or  stones  embedded 
in  it.  It  is  highly  desirable  to  preserve  a  smooth  finish  and  to  have 
the  interior  of  the  tunnel  free  from  roughness  which  will  tend  to 
check  the  velocity  of  the  water. 

Inverted  Siphons. — An  inverted  siphon  or  " siphon"  as  it  is  more 
frequently  termed,  is  used  for  conducting  water  across  depressions 
or  under  streams.  It  consists  of  a  water-tight  pipe  or  conduit  usually 
laid  below  the  surface  of  the  ground  and  through  which  water  is 
carried  by  gravity.  Siphons  take  the  place  of  trestle  flumes  in 
crossing  depressions  or  streams.  The  question  as  to  which  method 
of  construction  is  most  feasible  depends  for  answer  upon  local  condi- 
tions in  each  particular  case.  (See  Plate  VII,  Fig.  B.) 

The  accompanying  Fig.  31  gives  the  principal  dimensions  of  one 
of  the  smaller  reinforced  concrete  siphons  for  carrying  a  distributing 
canal  under  a  roadway  on  the  North  Platte  project  in  Nebraska. 

Siphons  are  better  adapted  to  the  crossing  of  deep  ravines  or 
canyons  than  flumes  on  account  of  the  impracticability  and  cost  of 
constructing  and  maintaining  high  trestles.  They  are  also  better 
adapted  to  carrying  a  canal  across  a  stream  of  varying  depth  since 
they  permit  the  water  in  the  canal  being  carried  at  any  elevation, 
while  if  carried  by  a  flume  it  must  be  kept  above  the  high-water 
elevation  of  the  stream.  In  general,  siphons  are  susceptible  of  more 
permanent  construction  and  require  less  expense  for  operation  and 
maintenance  than  trestle  flumes. 

In  the  design  of  a  siphon  it  is  necessary  first  to  determine  the 
amount  of  pressure  or  head  to  which  it  will  be  subjected,  the  fall 
available  in  its  length  and  th  echaracter  of  the  material  in  which  it 


CANAL  STRUCTURES 


93 


94        PRINCIPLES  OF  IRRIGATION  ENGINEERING 

is  to  be  constructed.  The  first  two  are  necessary  to  arrive  at  the 
strength  and  size  of  conduit  to  be  used  and  can  be  determined  from 
a  profile  of  the  line.  A  knowledge  of  the  character  of  material  is 
necessary  to  enable  the  selection  of  proper  foundations  and  anchor- 
ages for  holding  the  conduit  in  place,  and  should  be  obtained  by 
careful  field  examinations  and  excavations  if  necessary. 

The  head  on  any  point  of  a  siphon  is  the  distance  from  that  point, 
measured  vertically,  to  the  hydraulic  gradient  between  the  intake 
and  outlet  of  the  siphon.  If  this  distance  be  expressed  in  feet  the 
pressure  p  in  pounds  per  square  foot  is  ^  =  62.5  h.  If  the  diameter 
of  the  pipe  is  d,  the  transverse  stress,  s,  in  pounds  acting  upon 
i  lineal  foot  of  the  wall  of  the  pipe  and  tending  to  rupture  it  is 

s=62.$h—    From  this  the  strength  of  pipe  or  conduit  required 

is  readily  computed. 

The  available  head  tending  to  overcome  friction  and  produce  flow 
in  the  pipe  is  the  difference  in  elevation  between  the  water  surfaces 
at  the  two  ends  of  the  pipe.  The  head  per  unit  length  of  pipe  is 
this  difference  in  elevation  divided  by  the  length  of  the  pipe.  From 
this  the  velocity  of  flow  can  be  computed  by  the  ordinary  formulae 
for  the  flow  of  water  in  pipes,  allowance  being  made  for  velocity  and 
entrance  head.  In  order  to  obtain  the  maximum  capacity  of  a 
siphon  there  should  be  a  depth  of  water,  in  the  canal  or  entry  chamber 
over  the  entrance  to  the  pipe  equal  to  the  sum  of  the  velocity  and 
entry  heads.  Or  the  upper  end  of  the  pipe  may  be  made  of  larger 
sections  than  the  remaining  portion. 

The  foundation  under  a  siphon  should  be  sufficient  to  insure  safety 
against  settlement  under  the  combined  load  of  the  siphon  and  the 
water  which  it  carries.  It  should  be  firmly  anchored  in  place  in 
order  to  prevent  disturbances  which  would  have  a  tendency  to  cause 
leaks,  and  if  laid  under  a  stream  it  should  be  well  below  the  shifting 
bed  of  the  stream.  The  depth  to  which  a  siphon  should  be  placed 
below  the  surface  of  the  ground  outside  of  the  stream  bed  or  whether 
or  not  it  should  be  covered  at  all  will  depend  upon  local  conditions. 
A  covering  of  earth,  if  made  heavy  enough,  will  prevent  freezing 
during  extreme  cold  weather  and  tends  also  to  minimize  the  changes 
in  temperature  throughout  the  year  and  thus  reduce  contraction  and 
expansion.  Where  siphons  of  concrete  or  metal,  which  have  an 
appreciable  coefficient  of  expansion  are  subjected  to  considerable 
changes  in  temperature,  they  should  be  provided  with  expansion 
joints  at  frequent  intervals.  All  siphons,  where  possible,  should 


CANAL  STRUCTURES  95 

be  provided  with  means  for  emptying  them  for  purposes  of  examina- 
tion and  repairs  when  necessary. 

The  materials  from  which  siphons  are  commonly  constructed  are 
wood,  steel,  or  iron,  and  masonry,  including  plain  and  reinforced 
concrete. 

Wooden  siphons  are  commonly  constructed  in  the  form  of  wood 
stave  pipe,  the  necessary  strength  to  resist  the  pressure  imposed  upon 
them  being  given  by  iron  or  steel  bands.  The  size  and  spacing  of  these 
bands  are  dependent  upon  the  size  of  pipe  and  the  amount  of  head 
upon  it.  Siphons  of  wood  stave  pipe  are  being  operated  under  heads 
of  100  ft.  or  more.  On  account  of  the  wood  staves  being  saturated 
with  water  they  are  not  subject  to  decay  to  any  marked  degree,  so 
that  the  life  of  such  a  siphon  is  practically  the  life  of  the  metal  bands. 

Siphons  of  steel  or  wrought  iron  may  be  used  under  any  desirable 
heads,  cost  being  practically  the  only  limit.  For  extreme  heads,  say 
from  200  ft.  upward,  these  materials,  on  account  of  their  high  tensile 
strength,  seem  to  be  the  most  practicable.  In  using  steel  or  iron  pipes 
it  is  customary  to  cover  them  with  some  form  of  coating,  such  as  coal 
tar  or  asphaltum  compounds  in  order  to  protect  them  from  corrosion. 
A  siphon  recently  constructed  by  the  United  States  Reclamation 
Service  on  the  Uncompahgre  Valley  Project,  Colorado,  is  made  of 
practically  pure  iron.  This  siphon  is  approximately  3,700  ft.  in 
length,  26  in.  in  diameter,  and  is  subjected  to  a  maximum  head  of 
about  200  ft.  Pure  iron  was  used  upon  the  theory  that  this  material 
will  better  withstand  the  corrosive  action  of  certain  alkali  salts  con- 
tained in  the  soil  in  which  the  pipe  is  laid. 

Masonry  siphons,  except  when  reinforced,  are  practicable  for  low 
heads  only.  Reinforced  concrete  siphons  have  been  constructed  and 
are  being  successfully  operated  under  heads  up  to  about  100  ft.  In 
constructing  reinforced  concrete  siphons  especial  care  must  be  taken 
to  make  a  dense,  non-porous  concrete,  in  order  to  prevent  leakage. 
Additional  water-tightness  can  also  be  obtained  by  plastering  the 
interior  of  the  pipe  with  a  rich  mortar  of  cement  and  sand.  Suf- 
ficient steel  reinforcement  must  be  used  to  withstand  the  entire  water 
pressure  with  a  reasonable  factor  of  safety. 

A  combination  of  tunnel  and  siphon  is  occasionally  necessary 
in  connection  with  large  irrigation  works.  One  of  the  most  notable 
examples  of  this  kind  is  the  tunnel  under  Colorado  River  near  the 
town  of  Yuma,  Arizona,  where  the  main  line  of  the  irrigating  canal 
is  taken  out  on  the  California  side,  flows  southerly  to  a  point  opposite 
Yuma,  and  then  is  carried  under  the  river  by  means  of  a  tunnel,  water 


96        PRINCIPLES  OF  IRRIGATION  ENGINEERING 

rising  on  the  Arizona  side,  and  continuing  in  the  main  line,  with 
slight  loss  of  head.  There  thus  results  a  tunnel  under  pressure  which 
is  in  effect  an  inverted  siphon  shown  in  Fig.  32. 

This  tunnel  was  driven  through  partly  indurated  sands  beneath 
the  bed  of  the  river  by  the  use  of  compressed  air;  it  is  nearly  1,000 
ft.  in  length  and  14  ft.  inside  diameter.  Similar  less  expensive 
tunnels  are  occasionally  necessary  in  passing  under  the  beds  of 
streams,  but  as  a  rule  these  are  built  in  the  arid  regions  during 
the  time  of  year  when  the  streams  are  dry,  or  the  flow  is  so  small 
that  it  can  be  carried  in  a  flume  across  the  point  of  construction 


Arizona 


California 


700  600  500  400  300 

Distances  from  California  Shaft 


100 


FIG.  32. — Vertical  section  of  siphon  or  tunnel  under  Colorado  River,   Yuma 

Project,  Arizona. 

and  the  tunnel  built  in  the  open.  Still  smaller  structures  which 
can  hardly  be  termed  tunnels  are  frequently  built  to  permit  the 
passage  of  canals  under  a  depressed  railroad  track,  or  in  other 
localities  where  it  is  not  practicable  to  carry  the  water  on  grade. 

Bridges. — Where  canals  are  constructed  across  public  or  private 
roads,  so  as  to  interfere  with  ordinary  transportation,  bridges  must 
be  provided.  Whether  or  not  these  structures  are  built  by  public  or 
private  interests,  or  by  the  owners  of  a  canal  system,  are  matters  of 
detail  which  may  vary  in  individual  cases.  It  must  be  recognized, 
however,  that  they  are  necessary  and  sooner  or  later  must  be  con- 


CANAL  STRUCTURES  97 

structed.  By  whomsoever  built,  provisions  should  be  made  that  a 
type  of  bridge  be  adopted  that  will  not  interfere  with  the  operation 
and  maintenance  of  the  canals.  In  order  to  accomplish  this  in  a  satis- 
factory manner  the  designer  of  a  canal  system  should  also  provide,  or 
at  least  approve,  the  plans  for  bridges  which  may  be  constructed 
across  it. 

Aside  from  the  general  appearance  of  a  bridge,  which  is  an  item 
worthy  of  consideration  in  a  prosperous  community,  the  principal 
point  for  consideration  is  that  they  shall  not  interfere  with  the  flow 
of  water  in  the  canal.  To  insure  this  they  must  be  constructed  well 
above  the  maximum  high-water  surface.  A  safe  rule  to  follow  in 
this  is  to  make  the  height  of  the  bottom  of  the  floor  system  above 
the  maximum  water  surface  equal  to  the  free  board  of  the  canal. 
On  large  main  canals,  where  bridges  of  considerable  lengths  are  re- 
quired, the  question  whether  piers  or  center  bents  may  be  constructed 
in  the  canal  or  whether  a  clear  span  should  be  used  depends  upon  local 
conditions.  If  a  canal  carries  large  quantities  of  silt  or  debris,  any 
obstruction  is  likely  to  prove  a  menace  to  the  free  flow  of  water. 
Floating  weeds,  such  as  are  found  in  many  sections  of  the  west,  are 
especially  dangerous  and  may  obstruct  the  channel  to  such  an  extent 
that  water  will  be  forced  over  its  banks.  Where  the  water  is  clear 
and  does  not  carry  floating  materials,  center  bents  may  be  used 
without  detrimental  effects. 

The  kind  of  bridge  to  be  used,  whether  wood,  steel,  or  concrete, 
will  depend  upon  the  permanency  of  the  structure  required  and  the 
relative  costs  of  the  various  materials  in  the  particular  locality.  In 
the  design  of  bridges  consideration  should  be  given  to  the  maximum 
loads  which  they  may  be  required  to  carry.  This  will  depend  upon 
the  nature  of  the  traffic  and  will  vary  in  different  sections.  The 
maximum  load  on  a  public  highway  bridge  should  not  exceed  one- 
fourth  or  one-fifth  of  the  ultimate  strength  of  the  bridge.  All 
crossings  over  canals  should  be  constructed  in  a  manner  not  to  inter- 
fere with  free  access  along  the  canal. 

Measuring  Devices. — The  amount  of  water  diverted  from  the 
source  of  supply  to  the  canals  and  also  the  amounts  delivered  from 
the  canals  for  irrigation  or  other  purposes,  should  be  determined 
for  the  proper  management  of  the  system.  The  quantity  drawn 
from  a  source  of  supply  must  be  known  in  order  to  determine  what 
is  available  for  use  and  to  properly  conserve  this  supply.  The 
various  amounts  diverted  from  the  canal  system  must  be  known 
in  order  to  ascertain  how  much  is  being  delivered  to  water  users 
7 


98       PRINCIPLES  OF  IRRIGATION  ENGINEERING 

under  the  canal  and  how  much  is  lost  or  wasted.  Whether  water 
be  disposed  of  at  a  unit  price  for  a  given  quantity  say  an  acre-foot, 
or  whether  it  is  paid  for  in  terms  of  the  area  irrigated,  a  knowledge 
of  the  quantities  delivered  is  essential. 

In  order  to  determine  the  amount  of  water  diverted  to  and  from 
a  canal  system  each  diversion  structure  should  be  provided  with 
some  means  of  ascertaining  the  amount  of  water  which  it  delivers. 
In  this  connection  it  is  well  to  state  at  the  outset  that  water  measure- 
ments under  the  conditions  that  exist  in  practical  irrigation  are 
liable  to  serious  inaccuracies  and  that  improvement  in  this  particular 
branch  of  irrigation  work  is  urgently  needed.  The  inaccuracies  of 
our  present  methods,  however,  do  not  justify  their  neglect  nor 
discontinuance. 

In  general,  measuring  devices  for  use  on  canals  may  be  brought 
under  four  classes;  namely,  submerged  orifices,  weirs,  rating  flumes, 
and  mechanical  meters.  The  factors  involved  in  the  use  of  sub- 
merged orifices  are  the  size  of  the  orifice  and  the  head  upon  it. 
Where  a  constant  head  can  be  maintained  fairly  accurate  results 
can  be  obtained,  the  difficulty,  however,  is  to  maintain  this  constant 
head.  This  method  of  measurement  is  commonly  used  to  determine 
the  amount  of  water  passing  large  headgates,  the  quantity  of  dis- 
charge, Q,  being  computed  from  the  formula  Q  =  AC\/2gh.  Where 
A  is  the  area  of  opening,  g  the  acceleration  of  gravity  in  feet  per 
second,  h  the  head,  and  C  a  constant  depending  upon  the  shape  of 
the  opening.  Submerged  orifices  are  also  sometimes  used  to  de- 
termine the  amount  of  water  diverted  into  small  canals,  the  head 
being  determined  by  taking  the  difference  in  elevation  of  the  water 
surfaces  above  and  below  the  orifice  by  means  of  fixed  gages.  This 
form  of  apparatus  has  the  advantage  of  not  requiring  any  consider- 
able amount  of  fall  and  can  be  used  where  it  is  necessary  to  hold 
up  the  water  surface  in  order  to  cover  the  maximum  area  of  land. 
Where  low  heads  are  used  the  results  computed  from  head  and 
area  of  opening  are  subject  to  considerable  error. 

One  of  the  most  convenient  and  accurate  methods  of  determining 
the  discharge  into  a  small  canal  is  by  means  of  a  weir.  The  depth 
of  water  flowing  over  a  weir  can  be  shown  with  reasonable  accuracy 
by  means  of  a  gage  and  from  the  gage  reading  the  quantity  flowing 
can  be  readily  determined.  One  objection  to  the  use  of  weirs  is 
that  they  require  a  loss  of  head  from  the  main  canal  to  the-  lateral 
equal  to  approximately  the  depth  of  water  flowing  over  the  weir. 
In  exceptionally  flat  countries  a  drop  of  a  few  inches  in  the  lateral 


CANAL  STRUCTURES  99 

may  mean  the  loss  of  a  considerable  amount  of  land.  For  this 
reason  it  is  not  always  practicable  to  install  weirs  at  the  head  of 
laterals. 

Weirs  must  be  kept  in  good  repair  in  order  to  obtain  reliable 
results.  The  required  conditions  as  to  fall  and  contraction  of  the 
channel  must  be  maintained,  this  usually  requiring  frequent  atten- 
tion. The  smaller  weirs  are  rapidly  obstructed  by  silt,  the  bottom 
is  built  up  and  the  end  contractions  are  partly  suppressed.  Fre- 
quently the  smaller  canals  or  laterals  below  the  weirs  become  choked, 
backing  the  water  up  on  the  crest  of  the  weir.  Continuous  attention 
is  required  on  the  part  of  a  well-trained  force  of  canal  men  to  keep 
these  in  proper  condition. 

A  less  accurate,  but  more  simple  method  of  measuring  the  flow 
is  by  means  of  a  rating  flume  placed  in  the  canal,  whose  waters  are 
to  be  measured,  a  short  distance  below  the  head.  This  flume  may 
be  of  either  wood  or  concrete  and  its  depth  should  be  sufficient  to 
carry  the  desired  quantity  of  water.  Its  width  is  ordinarily  about 
the  same  as  that  of  the  canal.  The  capacities  of  the  flume  for 
different  depths  of  water  are  determined  by  calibration,  that  is, 
by  measuring  the  discharges  at  various  depths  by  means  of  a  weir 
or  current  meter.  Flumes,  like  submerged  orifices,  require  but 
little  head  for  their  operation,  and  for  this  reason  can  be  used  where 
weirs  are  not  applicable. 

One  of  the  chief  objections  to  any  of  the  above  measuring  devices 
is  that  no  account  is  taken  of  changes  in  flow  due  to  variations  in 
the  head  of  the  canal.  In  order  that  these  variations  be  shown  it  is 
necessary  that  they  be  equipped  with  self-recording  water-stage 
registers,  which,  for  a  large  canal  system,  are  expensive,  both  to 
install  and  to  maintain. 

Mechanical  meters  consist  of  some  form  of  revolving  wrheel  which 
is  operated  by  the  current  and  whose  velocity  of  rotation  varies 
with  the  velocity  of  flow.  The  apparatus  is  placed  in  a  contracted 
section  of  the  canal,  built  of  wood  or  masonry.  The  revolutions 
of  the  wheel  are  graduated  in  terms  of  the  quantity  of  water  dis- 
charged, either  in  second-feet  or  acre-feet. 

A  form  of  self-measuring  apparatus  now  being  tried  on  some  of 
the  projects  of  the  United  States  Reclamation  Service  registers  the 
amount  of  water  delivered  in  acre-feet. 

In  the  use  of  the  various  forms  of  wrater-measuring  devices  much 
depends  upon  the  ability,  judgment,  and  skill  of  the  persons  using 
them.  The  essential  thing  in  constructing  a  canal  system  is  that 


100      PRINCIPLES  OF  IRRIGATION  ENGINEERING 

some  form  of  measuring  device  should  be  installed.  The  type 
selected  for  any  canal  system  should  be  that  best  suited  to  the  con- 
ditions which  prevail  on  that  particular  system. 

Screens. — It  is  necessary  to  screen  the  inlets  to  all  pipes  and 
culverts  to  prevent  floating  material  being  carried  into  them,  and 
to  exclude  fish  at  the  head  of  canals  taking  water  from  perennial 
streams.  In  the  United  States  it  is  usually  required  by  state  law 
that  fish  screens  be  installed.  The  western  states  as  a  rule  require 
that  the  bars  of  these  screens  be  not  more  than  1/2  in.  apart.  This 
results  in  catching  floating  leaves,  sticks,  grass,  and  moss  so  that 
the  screens  are  quickly  clogged  and  the  canal  banks  may  be  flooded 
unless  the  screens  are  watched  constantly,  or  some  automatic  device 
is  provided. 

Screens  should  consist  of  nearly  vertical  bars  without  any  cross 
bars  near  the  surface  which  can  catch  the  teeth  of  a  rake  or  other 
tool  used  for  cleaning.  The  most  successful  screen  so  far  known  is 
that  consisting  of  iron  bars  1/2  in.  wide  and  2  in.  deep,  arranged  as  a 
grill,  inclined  at  an  angle  of  one  in  four,  and  with  a  footway  near 
the  top  from  which  the  operator  can  work. 

Protection  of  Canal  Structures. — On  account  of  the  important 
functions  of  canal  structures  and  the  magnitude  of  the  damage  which 
may  result  from  their  failure,  especial  care  should  be  taken  for  their 
protection.  The  principal  causes  of  failure  which  must  be  guarded 
against  are  erosion  and  seepage.  These  causes  are  common  to 
practically  all  classes  of  structures  which  are  used  for  controlling 
or  regulating  thJ  flow  of  water.  The  general  principles  applying  to 
one  case  are,  therefore,  equally  applicable  to  another. 

Where  the  section  of  a  waterway  or  canal  is  changed  or  where  the 
velocity  of  flow  is  increased,  one  or  both  of  which  may  occur  at  head- 
gates,  checks,  drops,  and  diversion  structures,  there  is  a  tendency 
to  set  up  eddy  currents  or  disturbances  which  may  cause  erosion  of 
the  sides  or  bottoms  of  the  channel.  This  erosion  may  take  place 
either  above  or  below  a  structure  and  cause  a  dangerous  condition 
to  exist  before  it  is  discovered.  To  avoid  this  source  of  damages  it 
is  necessary  first  to  so  design  structures  that  the  variations  from  the 
normal  canal  section  will  be  a  minimum,  and  second  to  thoroughly 
protect  the  channel  above  and  below  them. 

When  water  is  carried  over  a  drop  an  increase  in  the  velocity  of 
flow  cannot  be  avoided.  This  increased  velocity  must  be  reduced 
at  the  bottom  of  the  drop  and  the  channel  at  that  point  must  be 
sufficiently  protected  to  absorb  without  danger  the  energy  expended 


CANAL  STRUCTURES  101 

upon  it.  The  same  is  true  of  water  carried  through  turnouts  under 
any  considerable  head,  and  it  is  necessary  to  guard  against  erosion 
at  the  points  of  entrance  and  discharge  of  these  structures.  A  very 
satisfactory  form  of  channel  protection  is  rough  stone  paving  laid 
on  a  firm  foundation  and  the  joints  filled  with  concrete  mortar. 
The  advantage  of  rough  stone  is  that  it  checks  the  velocity  more 
effectively  than  a  smooth  paving. 

Seepage  along  the  sides  and  under  structures  should  be  guarded 
against  by  the  use  of  ample  cutoff  walls,  and  by  backfilling  around 
all  structures  with  impermeable  material  carefully  puddled  or  tamped 
into  place.  The  construction  of  projecting  rings  or  collars  on  a  turn- 
out pipe  will,  to  a  large  degree,  prevent  seepage  water  following 
along  the  outside  of  the  pipe.  Thin  narrow  buttress  walls,  carried 
up  along  the  outside  of  a  structure,  will  reduce  the  tendency  of  seep- 
age water  to  follow  around  the  structure.  Embankments  above 
structures,  especially  where  wing  walls  are  carried  into  them,  in 
addition  to  being  carefully  constructed  should  be  made  of  generous 
dimensions. 


CHAPTER  VI 
DISTRIBUTION  SYSTEMS 

Canals  and  Laterals. — The  term  "Canal  Systems"  applied  to 
irrigation  works  includes  all  channels  used  in  conveying  water  from 
the  source  of  supply  to  the  point  where  it  is  ultimately  delivered 
onto  the  land.  The  channels  included  in  a  canal  system  may  vary 
greatly  in  dimensions  and  have  capacities  ranging  from  above  1,000 
cu.  ft.  per  second  down  to  i  cu.  ft.  per  second  or  less.  The  various 
conduits  or  a  canal  system  are  usually  classified  under  the  general 
heads  of  canals,  laterals  or  distributaries  as  the  latter  are  sometimes 
called.  The  distinction  between  canals  and  laterals  is,  to  a  certain 
degree,  an  arbitrary  one.  In  general,  however,  the  term  canal  is 
applied  to  a  channel  which  carries  water  for  irrigation  but  from  which 
direct  diversion  of  water  onto  the  land  is  not  made.  The  term  lateral 
is  applied  to  a  channel  which  takes  water  from  the  side  of  the  canal 
and  carries  it  along  or  near  the  canal  and  out  onto  the  land  to  be 
irrigated. 

Canals  are  further  sub-divided  into  main  and  branch  canals.  A 
main  canal  is  one  which  carries  water  directly  from  the  source  of 
supply.  Branch  canals,  as  the  name  implies,  are  those  which  carry 
water  from  a  main  to  different  irrigable  areas.  Laterals  are  also  sub- 
divided into  main  and  branch  laterals.  The  terms  more  frequently 
used,  however,  in  this  connection,  are  laterals  and  sub-laterals;  a 
lateral  being  a  channel  which,  in  addition  to  distributing  water  from 
a  canal  directly  to  the  lands,  also  conveys  it  to  smaller  branch  or 
sub-laterals.  The  term  " Distribution  System"  is  intended  to  in- 
clude channels  which  carry  water  from  canals  and  distribute  it  onto 
the  lands. 

It  is  to  be  noted  that  the  definition  of  canals  and  laterals  takes  no 
account  of  the  relative  capacities  of  these  channels.  A  channel 
defined  as  a  lateral  may,  therefore,  have  several  times  the  capacity  of 
another  channel  properly  defined  as  a  canal,  i.e.,  the  main  canal  of  a 
system  taking  water  from  a  stream  or  reservoir  to  10,000  acres  may 
be  smaller  than  the  lateral  of  another  system  supplying  20,000  acres. 
or  more. 

102 


DISTRIBUTION  SYSTEMS  103 

General  Plan  of  Distribution  System. — The  requirement  of  a 
distribution  system  is  that  it  shall  be  capable  of  supplying  water  to 
all  irrigable  lands  under  the  canals.  In  general,  irrigable  lands  are 
divided  into  small  areas  or  individual  holdings,  and  an  adequate 
distribution  system  is  assumed  to  be  capable  of  delivering  water  to 
the  highest  point  of  each  of  these  small  areas.  The  plan  of  a  dis- 
tribution system  will  depend  upon  the  topographic  features  of  the 
tract  to  be  irrigated,  and,  in  general,  each  system  must  be  modified  to 
suit  peculiar  conditions. 

For  irrigation  requirements  lands  may  be  considered  under  three 
classes:,  (a)  uniformly  sloping  planes,  (b)  ridges,  (c)  undulating  areas, 
portions  of  which  are  higher  than  any  other  lands  immediately 
adjacent  to  them.  The  problems  met  in  planning  a  distribution 
system  are  those  of  reaching  each  of  the  above-described  areas  with 
a  minimum  amount  of  construction  work. 

Uniformly  sloping  planes  allow  great  latitude  of  design  in  distribu- ' 
tion  canals  and  permit  ordinarily  the  laying  out  of  rectangular  or 
parallel  systems  of  laterals.  Where  possible  these  laterals  should  be 
located  along  land  sub-divisions  and  property  lines.  This  plan  of 
location  avoids  the  necessity  of  cutting  across  individual  farms  by 
canals  and  frequently  reduces  the  amount  of  good  land  otherwise 
required  for  right-of-way  for  canals.  Systems  of  this  kind  should 
have  the  laterals  or  sub-laterals  near  enough  together  so  that  water 
can  be  carried  over  the  lands  from  one  farm  to  the  next  adjacent  to  it. 
Where  topographic  conditions  are  favorable  the  area  between  two 
laterals  may  be  covered  partly  from  one  side  and  partly  from  the 
other. 

Ridges  must  be  reached  by  laterals  constructed  along  their  highest 
portions.  These  laterals  must  necessarily  conform  to  the  direction 
of  the  ridges  so  that  water  may  be  carried  from  either  side  down  the 
slopes  to  the  intervening  depressions.  This  necessitates  an  appar- 
ently irregular  plan,  the  laterals  crossing  the  fields. 

Undulating  areas  are  by  far  the  most  difficult  to  irrigate  and  no 
general  plan  is  applicable  for  different  cases.  High  spots  above  the 
level  of  adjacent  lands  may  be  reached  by  means  of  ditches  or  flumes 
built  above  the  surface  of  the  ground.  Siphons  or  pressure  pipes  are 
also  used  to  carry  water  across  low  depressions  to  the  higher  lands. 
The  choice  of  one  of  the  various  plans  which  may  be  used  for  reach- 
ing isolated  high  areas  ordinarily  requires  comparative  studies  of 
cost  as  well  as  consideration  of  their  relative  merits  for  permanency 
and  efficiency. 


104      PRINCIPLES  OF  IRRIGATION  ENGINEERING 

The  necessity  of  a  carefully  considered  plan  of  works  for  the  dis- 
tribution of  water  cannot  be  too  strongly  insisted  upon.  The  dis- 
tribution system  is  to  an  irrigation  project  what  a  delivery  system  is 
to  a  transportation  company  in  carrying  on  its  business.  If  a  dis- 
tribution system  fails  or  is  inefficient,  the  entire  irrigation  system  fails 
or  is  rendered  inefficient  to  a  greater  or  less  degree.  Mistakes  made 
in  the  original  planning  and  laying  out  of  a  lateral  system  ordinarily 
cannot  be  corrected  without  damage  to  improvements  and  a  corre- 
sponding high  cost  for  making  changes.  The  ultimate  value  of  an 
irrigation  system  depends  upon  its  efficiency  in  supplying  the  needs 
of  the  water  user. 

Topographic  Surveys  for  Lateral  Systems. — On  small  areas,  or 
areas  the  topography  of  which  is  comparatively  simple,  the  most 
feasible  plan  for  a  lateral  system  can  ordinarily  be  determined  with- 
out extensive  topographic  surveys,  the  method  followed  being  to 
determine  the  elevation  of  the  commanding  points  on  the  area  and 
using  these  as  a  basis  for  the  location  of  the  main  laterals.  In 
making  these  preliminary  studies  the  principal  point  to  be  considered 
is  to  locate  the  main  laterals  so  that  they  will  command  as  much  as 
possible  of  the  irrigable  area.  In  preparing  plans  in  this  manner 
alternate  surveys  should  be  freely  made  in  order  that  all  possible 
and  feasible  plans  may  be  considered. 

For  large  areas,  or  areas  where  the  topography  is  complex,  contour 
maps  should  be  prepared  as  a  basis  for  laying  out  lateral  systems. 
The  principal  objection  to  a  topographic  survey  for  this  purpose  is  its 
cost.  One  of  the  first  points  which  must  be  decided  is  whether  or  not 
the  topography  is  such  that  the  advantages  to  be  gained  in  the  effi- 
ciency of  the  system  are  sufficient  to  justify  the  expense  of  such 
surveys.  The  advantages  of  topographic  surveys  as  a  basis  for  plan- 
ning lateral  systems  are  as  follows:  (a)  They  show  the  general  slopes 
of  the  country,  give  at  once  the  amount  of  fall  which  is  available,  and 
serve  as  a  guide  for  the  general  direction  in  which  laterals  should  be 
constructed,  (b)  On  complex  topography,  such  as  broken  ridges  or 
isolated  high  areas,  they  indicate  what  lands  can  be  covered  by 
surface  canal  and  those  which  must  be  reached  by  means  of  flumes 
or  siphons,  (c)  Several  alternate  systems  of  laterals  can  be  laid 
out  on  a  carefully  prepared  contour  map  and  preliminary  estimates 
made  thereon,  at  a  much  less  cost  than  these  studies  can  be  carried 
on  in  the  field,  and  the  individual  areas  into  which  a  tract  must 
be  broken  in  order  to  reach  all  points  can  be  readily  determined, 
(d)  Topographic  surveys,  in  addition  to  being  an  aid  in  the  designing 


DISTRIBUTION  SYSTEMS  105 

and  locating  of  a  lateral  system,  are  of  benefit  in  future  maintenance 
as  they  indicate,  in  a  general  way,  how  irrigation  can  best  be  carried 
on  after  the  system  has  been  constructed. 

Where  the  topography  is  such  as  to  permit  of  various  plans  being 
used  the  cost  of  a  topographic  survey  of  the  lands  to  be  covered  is 
justified,  and,  in  most  cases,  there  is  an  actual  saving  by  this  pro- 
cedure, due  to  the  more  economic  method  in  which  engineering 
studies  can  be  made  and  the  greater  efficiency  of  the  system  that  can 
be  designed.  In  working  from  topographic  maps  the  engineer  has 
before  him,  in  condensed  form,  the  entire  irrigable  areas  and  is  thus 
enabled  to  project  thereon  all  possible  plans.  In  working  directly 
from  the  ground,  it  is  impossible,  especially  if  the  topography  is  com- 
plex, to  see  all  of  the  various  methods  which  may  be  used  and  some 
of  the  most  advantageous  features  of  a  design  may  be  overlooked. 

Topographic  maps  to  be  used  for  designing  a  lateral  system 
should  be  constructed  on  a  sufficiently  large  scale  to  enable  the 
various  works  to  be  projected  thereon.  The  contour  interval 
should  be  small  enough  to  enable  one  to  determine  from  the  map, 
to  within  a  reasonable  degree  of  accuracy,  the  courses  of  the  various 
laterals,  the  location  of  drops  and  other  structures,  as  well  as  the 
areas  which  can  be  brought  under  any  particular  lateral.  The 
scale  and  contour  interval  best  adapted  to  a  particular  case  will 
depend  upon  the  nature  of  the  country,  the  most  complex  topog- 
raphy requiring  the  smaller  contour  interval  and  larger  scale.  In 
general,  maps  to  be  used  for  lateral  locations  should  have  a  contour 
interval  not  exceeding  i  ft.,  and  a  scale  ranging  from  400  to  1,000 
ft.  per  inch. 

Where  contour  maps  are  prepared  for  aid  in  designing  a  lateral 
system,  attention  should  be  given  to  other  features  which  will 
make  them  valuable  for  future  use  in  connection  with  operation 
and  maintenance  work.  The  contours  should  be  projected  upon 
an  accurate  base  map,  which  should  show,  in  so  far  as  they  can  be 
located,  the  positions  of  all  public  and  private  land  lines  and  corners. 

Capacity  of  Laterals. — The  discussion  of  capacity  of  canals, 
given  on  page  39,  applies  also  to  laterals  and  distributaries.  In 
the  design  of  the  smaller  distribution  canals,  however,  some  factors 
must  be  given  consideration  which  are  insignificant  and  may  be 
omitted  for  larger  canals.  One  of  these  already  mentioned  is  that 
of  the  maximum  duty  of  a  canal.  A  canal  which  is  used  only  a 
portion  of  the  time,  as  is  commonly  the  case  with  a  small  lateral, 
must  have  a  greater  capacity  per  unit  area  of  land  covered  by  it 


106      PRINCIPLES  OF  IRRIGATION  ENGINEERING 

than  one  which  is  operated  continuously.  Other  and  equally 
important  factors  in  small  laterals  are  evaporation  and  seepage 
losses. 

Evaporation  losses  from  small  bodies  of  water,  climatic  con- 
ditions being  practically  the  same,  will  vary  almost  directly  as  the 
area  of  water  surface.  The  percentage  lost  from  a  small  canal  on 
account  of  its  less  depth  will  exceed  that  from  a  large  canal.  Evapo- 
ration losses  from  the  direct  water  surface  in  canals  are,  however, 
relatively  small  compared  with  seepage  losses.  The  proportion 
of  water  lost  by  seepage  is  also  much  greater  in  small  than  in  large 
canals.  The  results  of  observation  on  this  subject,  while  not  con- 
clusive, seem  to  show  that  the  average  seepage  losses  from  canals 
carrying  more  than  100  cu.  ft.  per  second  is  less  than  i  per  cent, 
per  mile  of  canal,  while  for  canals  carrying  less  than  10  cu.  ft.  per 
second  the  average  losses  exceed  10  per  cent,  per  mile.  On  account 
of  the  higher  seepage  losses  the  allowance  made  for  them  in  fixing 
the  capacity  of  a  small  lateral  must  be  relatively  much  greater 
than  for  a  large  canal.  Just  what  these  losses  will  amount  to  in 
any  particular  case  will  depend  upon  the  character  of  the  material 
forming  the  waterway  of  the  canal.  It  must  be  remembered, 
however,  that  seepage  losses  are  constantly  taking  place  from 
earthen  canals  and  that  while  the  percentage  of  loss  may  be  so  small 
as  to  be  negligible  in  very  large  canals  it  may  be  sufficient  to  materi- 
ally effect  the  capacity  of  a  small  lateral. 

Some  investigations  have  been  made  to  determine  seepage  losses 
in  terms  of  the  wetted  area.  These  results  show  losses  varying 
from  about  0.25  to  6.0  cu.  ft.  of  water  per  square  foot  of  wetted  area 
per  day.  In  most  cases,  however,  the  daily  rate  of  seepage  varies 
from  about  0.5  to  1.5  cu.  ft.  per  square  foot  of  wetted  area.  Data 
on  seepage  losses,  in  this  form,  are  the  most  convenient  for  practical 
use  in  determining  comparative  losses  in  various  materials.  They 
can  readily  be  reduced  to  a  percentage  of  total  flow  per  mile  for 
any  particular  size  and  shape  of  canal. 

An  illustration  showing  the  method  of  taking  account  of  seepage 
losses  may  be  of  interest.  Let  it  be  required  to  deliver  at  the  lower 
end  of  a  lateral  10  miles  long,  water  at  the  rate  of  20  cu.  ft.  per 
second.  Assume  the  seepage  losses  to  be  3  per  cent,  per  mile. 
How  much  water  must  be  supplied  to  the  head  of  the  lateral? 
The  safe  and  quick  method  of  ccmputing  this  would  be:  multiply 
the  percentage  of  less  per  mile  by  the  length  of  canal  in  miles, 
which  gives  a  total  loss  of  30  per  cent.  This  result  is  slightly  in 


DISTRIBUTION  SYSTEMS  107 

excess  of  the  actual  theoretical  losses,  since  no  account  has  been 
taken  of  reduced  amounts  being  carried  at  each  succeeding  mile. 
The  actual  amount  reaching  the  lower  end  of  the  lateral,  computed 
upon  the  basis  of  3  per  cent,  of  that  delivered  to  it  being  lost  in 
each  mile,  is  o.g710  =  .737  or  73.7  per  cent,  approximately.  The 
quantity  which  must  be  delivered  to  the  head  of  the  lateral  to 
supply  20  cu.  ft.  per  second  at  its  lower  end  is  20  divided  by  .737 
=  27.1  cu.  ft.  per  second. 

The  minimum  amount  of  water  by  which  irrigation  can  be  effec- 
tively and  economically  carried  on  is  sometimes  called  an  irrigation 
head.  It  will  vary  for  different  kinds  of  soil  and  crops.  In  general, 
however,  it  may  be  said  to  range  from  i  to  10  second-feet. 

The  capacity  of  a  lateral,  whatever  the  area  under  it  may  be,  must 
be  large  enough  to  carry  enough  irrigation  heads  or  sufficient  water 
to  permit  of  economic  irrigation.  In  order  to  carry  on  irrigation 
economically  and  to  get  over  the  ground  satisfactorily,  sufficient 
water  must  be  supplied  to  permit  of  a  cultivated  area  or  field  between 
checks  or  ridges  being  entirely  covered  before  that  portion  to  which 
water  is  turned  first  becomes  unduly  saturated. 

The  growth  of  grass  and  weeds  in  laterals  tends  to  materially 
reduce  their  capacity  and  should  be  taken  into  account  when  design- 
ing a  distribution  system.  This  reduction,  while  small  in  sectional 
area,  in  some  cases  may  be  sufficient  to  reduce  the  velocity  and 
consequent  capacity  of  a  canal  by  as  much  as  40  or  50  per  cent., 
thus  rendering  it  too  small  to  carry  an  effective  irrigation  head. 

Location  of  Laterals. — The  problems  involved  in  the  location  of 
small  laterals  differs  in  some  respects  materially  from  those  met  in 
the  location  of  larger  canals.  The  principal  function  of  a  main  or 
branch  canal  is  to  carry  water  from  the  source  of  supply  to  the 
smaller  distributaries  or  laterals.  The  importance  of  main  and 
branch  canals  as  a  part  of  a  system  demands  that  they  be  given  the 
safest  possible  location  which  the  nature  of  the  country  and  reason- 
able limits  of  costs  will  allow.  Since  water  is  ordinarily  not  diverted 
from  these  canals  directly  to  the  lands  it  is  unnecessary  to  carry 
them  above  the  surface  of  the  ground  in  order  to  reach  especially 
favorable  points  for  diversion. 

The  function  of  a  distributary  or  lateral  is  to  carry  water  directly 
to  the  irrigable  lands.  The  location  must  be  so  chosen  that  the 
maximum  area  can  be  watered.  Favorable  points  for  diversion 
must  also  be  considered  and  the  laterals  brought  to  them.  The 
general  elevation  of  laterals  must  be  sufficiently  high  to  enable  the 


108      PRINCIPLES  OF  IRRIGATION  ENGINEERING 

water  surface  to  be  kept  above  the  adjacent  lands.  Where  necessary 
in  order  to  accomplish  this  the  waterways  of  laterals  must  be  con- 
structed in  embankment.  In  other  words,  the  main  object  to  be 
considered  in  lateral  location  is  the  delivery  of  water  to  the  greatest 
possible  area. 

Safety  against  breaks  in  laterals  should  be  insured  by  properly 
planned  and  constructed  banks,  rather  than  by  reducing  the  amount 
of  land  under  them  to  obtain  a  more  favorable  location.  It  is 
frequently  necessary  to  compare  the  difference  in  the  cost  of  con- 
struction over  two  different  locations  with  the  value  of  extra  land 
which  can  be  reached  if  the  more  difficult  route  be  chosen.  In 
making  such  comparisons  it  must  be  remembered  that  the  value  of 
lands,  when  once  brought  under  irrigation,  may  be  expected  to  con- 
tinue to  increase,  and  for  this  reason  the  greatest  development  pos- 
sible should  be  considered. 

On  uniformly  sloping  areas,  all  of  which  can  be  watered  by  two 
or  more  systems  of  laterals,  efficiency  of  system  and  economy  of 
construction  should  be  considered.  These  questions  may  involve 
the  laying  out  of  alternate  systems  and  the  making  of  estimates 
on  each.  On  flat  slopes,  where  the  velocities  are  necessarily  low 
there  is  usually  an  economy  in  serving  as  much  land  as  possible  from 
a  single  lateral,  on  account  of  the  larger  cross-section  required  and 
correspondingly  higher  velocities  which  may  be  attained. 

Cross-section  of  Laterals. — In  fixing  the  cross-section  of  a  lateral 
there  should  be  considered  (a)  the  character  of  the  material;  (b)  the 
method  by  which  it  is  to  be  excavated,  and  (c)  the  grade  or  slope. 

Lateral  ditches  are  for  the  most  part  constructed  in  fertile  soils 
which  will  not  support  steep  banks.  Ordinarily  it  is  not  practicable 
to  construct  slopes  steeper  than  i  to  i,  and,  except  in  very  rare  cases, 
is  it  necessary  to  make  them  flatter  than  2  to  i.  If  laterals  are  built 
by  means  of  teams  and  scrapers,  slopes  of  i  1/2  or  2  horizontal  to 
i  vertical  are  the  most  practicable  from  the  standpoint  of  con- 
struction, since  these  slopes  facilitate  team  work  in  taking  out  the 
excavation.  If,  on  the  other  hand,  the  work  is  to  be  done  by 
excavating  machinery,  slopes  as  steep  as  i  to  i  may  be  found  to 
an  advantage.  In  permeable  soils,  where  seepage  losses  are  high, 
as  steep  slopes  as  possible  should  be  used  in  order  to  reduce  the 
amount  of  wetted  area  to  a  minimum. 

The  ratio  of  bottom  width  to  the  depth  of  water  is  an  important 
factor  in  determining  the  velocity  of  flow.  Where  the  land  is  nearly 
level  and  it  is  necessary  to  conserve  grade  as  much  as  possible,  a 


DISTRIBUTION  SYSTEMS  109 

comparatively  narrow  and  deep  section  is  the  most  advantageous. 
Where  the  fall  of  the  land  is  considerable  and  it  is  necessary  to  reduce 
velocities,  much  can  be  accomplished  by  adopting  a  wide  and 
shallow  section.  In  fixing  the  ratio  of  width  to  depth,  account 
should  be  taken  of  the  method  by  which  excavation  is  to  be  carried 
on  and  also  the  character  of  the  material  for  resisting  seepage. 

The  top  width  of  banks  and  their  height  above  the  water  surface 
will  depend  upon  the  stability  of  the  material  of  which  they  are 
constructed,  and  the  degree  of  safety  against  overtopping  which  it 
may  seem  desirable  to  adopt.  In  general,  the  top  width  of  banks,  for 
the  smaller  laterals,  need  not  exceed  about  3  ft.  The  height  above 
the  water  surface  should  be  sufficient  to  give  stability  to  the  embank- 
ment and  serve  as  a  protection  against  overtopping  in  case  of  a 
sudden  rise  in  the  canal.  It  is  not  an  uncommon  occurrence  for  a 
lateral,  especially  a  small  one,  to  be  required  to  carry  temporarily 
an  overload  of  50  per  cent,  above  its  figured  capacity  and  provisions 
should  be  made  for  such  emergencies.  Where  the  waterway  is  all, 
or  a  great  part,  in  fill,  a  greater  height  of  free  board  should  be  allowed 
than  where  it  is  in  cut.  This  latter  precaution  is  necessary  to  give 
stability  and  provide  for  settlement  in  the  higher  embankments. 

Points  of  Delivery  of  Water. — The  location  of  points  where  water 
is  to  be  delivered  from  laterals  and  sub-laterals  to  the  lands  will  be 
determined  to  a  great  extent  by  the  topography  of  the  lands  to  be 
irrigated.  The  fundamental  requirement  is  that  these  points  be  so 
located  that  water  can  be  carried  from  them  over  the  maximum  area 
by  means  of  small  farm  ditches.  The  number  of  delivery  points 
should  be  as  small  as  possible  and  still  provide  ample  means  for 
reaching  th e  entire  irrigable  area.  B y  reducing  the  number  of  delivery 
points  to  the  minimum  required,  the  cost  of  construction,  operation 
and  maintenance  of  small  diversion  structures  is  reduced.  In  gen- 
eral, delivery  points  should  be  located  on  the  highest  lands  possible, 
or  in  other  words,  where  the  laterals  or  sub-laterals  are  entirely  or 
to  a  large  extent  in  excavation.  These  higher  points  are  as  a  rule 
more  favorable  for  delivery  of  water  to  the  lands  and  also  for  the  safe 
maintenance  of  structures. 

A  condition  which  frequently  arises  to  increase  the  number  of  de- 
livery points  of  a  lateral  is  that  where  the  irrigable  area  is  divided  into 
small  individual  holdings,  each  requiring  an  independent  water  outlet. 
Such  a  system  permits  the  amount  of  water  turned  to  each  user  to  be 
measured  and  controlled  and  prevents  the  necessity  of  water  users 
making  distribution  of  water  among  themselves.  Delivery  of  water 


110      PRINCIPLES  OF  IRRIGATION  ENGINEERING 

direct  to  each  user,  especially  where  lands  are  held  in  small  tracts  of 
from  10  to  20  acres,  requires  a  much  more  elaborate  and  costly  dis- 
tribution system  than  where  one  deliveiy  point  can  be  made  to  serve 
an  area  of  from  40  to  So  acres,  or  more. 

The  number  of  delivery  points  required  depends  upon  the  topog- 
raphy of  the  lands  to  be  irrigated,  the  size  of  individual  land  hold- 
ings and  the  policy  to  be  pursued  in  the  delivery  of  water,  that  is, 
whether  it  is  to  be  delivered  to  each  individual  or  to  associations  of 
water  users. 

The  question  cf  fixing  delivery  points  of  a  distribution  system  is 
one  which  requires  careful  study  and  consideration  in  each  individual 
case,  the  fundamental  principles  to  be  worked  out  in  these  studies 
being  to  reduce  the  number  of  delivery  points  to  the  fewest  prac- 
ticable and  still  provide  an  efficient  service  for  the  entire  irrigable 
acreage. 

Delivery  Box. — The  term  "Delivery  Box"  is  usually  applied  to  the 
structure  which  regulates  and  controls  the  distribution  of  water  from 
the  lateral  to  the  land  of  the  farmer.  It  is  the  last  link  in  the  system 
of  canals  and  distributaries  which  carries  water  from  the  source  of 
supply  to  the  area  upon  which  it  is  to  be  used.  The  requirements  of 
a  delivery  box  are  that  it  be  adequate  to  control  and  measure  the 
water  which  passes  it,  and  that  its  capacity  be  sufficient  to  deliver 
the  maximum  amount  of  water  required  for  irrigating  the  lands  under 
it.  Various  types  of  boxes  are  used  in  different  irrigation  systems 
and  special  forms  are  frequently  devised  to  meet  certain  conditions. 
It  is  impossible  to  say  that  any  one  type  is  superior  to  alt  others.  A 
fundamental  principle  which  should  be  borne  in  mind  is  that  delivery 
boxes  are  essentially  a  part  of  a  canal  system  and  should  therefore  be 
opened  and  closed  only  by  the  organization  which  operates  the  canal 
system.  They  should  be  so  constructed  that  should  it  be  found 
necessary,  interference  with  them  by  unauthorized  persons  can  be 
detected  and  prevented. 

The  amount  of  water  delivered  to  the  lands  can  be  measured  only 
at  the  point  of  delivery.  It  is  therefore  necessary  that  a  delivery 
box  be  provided  with  suitable  equipment  for  ascertaining  the  water 
which  passes  through  it,  if  record  of  the  amount  used  in  iirigation  is  to 
be  kept,  as  it  should  be  in  every  case. 

The  simplest  form  of  delivery  box  consists  of  a  rectangular  wooden 
structure  placed  in  the  side  or  bank  of  a  canal  or  lateral  and  provided 
with  an  opening  through  which  water  is  diverted.  When  not  in  use, 
the  opening  is  closed  by  means  of  boards  or  some  simple  form  of  gate 


PLATE  VIII 


FIG.  A. — Distributing  laterals  with  wooden  boxes  and  gates,    typical  of  the 
pioneer  work  in  irrigation.     Yakima  Project,  Wash. 


FIG.  B. — Concrete  box  and  drop  on  distributory   in  place  of  earlier  form  of 
wooden  construction.     Orland  Project,  Cal. 

(Facing  Page  no) 


PLATE  VIII 


FIG.  C. — Cast-iron  valves  on  distributing  systems  instead  of  the  usual  wooden 
gates.     Uncompahgre  Project,  Colo. 


FIG.  D. — Farmers'water  gates  on  inclined  concrete  slabs.     Sun  River 
Project,  Mont. 


DISTRIBUTION  SYSTEMS 


111 


which  can  be  raised  to  the  required  height  to  pass  the  quantity  of 
water  desired.  More  permanent  structures  of  the  same  type  are 
constructed  of  concrete  or  other  form  of  masonry,  and  the  openings 
closed  by  means  of  metal  gates.  Another  type  consists  of  a  covered 
box  of  wood  or  masonry  carried  through  the  banks  and  having  the 
upper  and  lower  ends  protected  so  as  to  prevent  erosion.  (See 
Plate  VIII.) 

The  forms  of  measuring  devices  commonly  used  are  weirs,  rating 
flumes  and  some  type  of  submerged  orifice  through  which  the  flow 


FIG.  33. — Plank    measuring  box  with  Cippoletti  weir  and  automatic  register. 

of  water  can  be  determined.  Where  there  is  sufficient  fall  to  permit 
its  being  used,  the  weir  is  perhaps  the  most  satisfactory,  cheap  and 
simple  device  for  measuring  relatively  small  flows,  such  as  are  com- 
monly turned  into  farm  ditches  and  the  smaller  laterals  and  sub- 
laterals.  For  this  purpose  both  the  rectangular  and  Cippoletti  weirs 
are  used  (Fig.  33).  The  latter  type  of  weir  possesses  some  advan- 
tage over  the  former  as  it  is  unnecessary  to  take  account  of  end 
contractions. 

A  rating  flume  ordinarily  consists  of  a  square  or  rectangular  box 
open  at  both  ends  and  placed  in  the  channel  so  as  to  form  the  water- 
way for  a  distance  of  several  feet.  The  flume  is  first  rated  for 


112      PRINCIPLES  OF  IRRIGATION  ENGINEERING 

various  depths  of  water  flowing  through  it  by  means  of  current 
meters,  weirs  or  other  suitable  measuring  devices.  For  convenience 
of  reference,  the  amount  of  discharge  for  different  depths  are 
commonly  shown  by  means  of  a  graphic  curve  or  table.  Measure- 
ments are  then  made  by  observing  the  depths  of  water  passing 
the  flume  and  taking  the  corresponding  discharge  from  thecurve 
or  table. 

A  submerged  orifice  consists  of  an  opening  through  which  water  is 
allowed  to  flow  under  a  small  pressure  or  head.  The  amount  of 
head,  if  the  orifice  has  a  free  discharge,  is  found  by  taking  the  height 
of  water  above  its  center,  or  if  the  lower  side  of  the  orifice  be  sub- 
merged, by  taking  the  difference  in  elevation  of  water  above  and 
below  the  orifice.  The  amount  of  discharge  depends  upon  the  head, 
size  of  orifice  and  the  form  of  the  upper  edge  of  the  opening,  whether 
square  or  round.  The  quantity  of  discharge  Q  may  be  computed 
from  the  expression  Q  =  AC\/gh  where  A  is  the  area  of  orifice,  C 
a  constant  depending  upon  the  form  of  the  upper  edge  of  the  opening, 
g  the  acceleration  of  gravity  in  feet  per  second,  h  the  head  in 
feet.  In  order  to  determine  accurately  the  amount  of  water  passing 
a  submerged  orifice,  the  value  of  C  for  that  particular  form  must 
be  previously  determined.  Roughly,  this  value  may  be  said  to  vary 
from  about  0.6  as  a  minimum  to  i.o  as  an  ultimate  maximum.  For 
a  more  complete  determination  of  the  flow  of  water  through  orifices, 
the  reader  is  referred  to  special  works  on  hydraulics. 

Automatic  devices  for  the  measurement  of  water  have  been  used  to 
a  small  extent.  They  consist  essentially  of  submerged  orifices  each 
provided  with  a  current  meter  for  measuring  the  velocity.  These 
devices  are  commonly  so  graduated  as  to  indicate  the  actual  amount 
of  water  passed  in  some  convenient  unit  of  measurement,  such  for 
example  as  the  acre-foot.  In  all  measuring  devices,  unless  they  are 
provided  with  automatic  registers,  serious  errors  are  apt  to  occur  on 
account  of  variable  heads,  frequently  found  in  the  laterals.  These 
errors  in  a  great  measure  can  be  overcome  for  weirs,  rating  flumes  and 
submerged  orifices  by  the  use  of  water-stage  registers  which  show  at 
all  times  the  head  in  the  canal. 

The  expense  of  refined  measuring  apparatus  is  usually  large  and 
it  is  frequently  a  question  whether  this  is  justifiable.  The  reply 
depends  almost  wholly  on  the  value  of  water  in  the  particular 
locality  where  they  are  to  be  used.  For  this  reason  in  determin- 
ing the  type  of  measuring  device,  it  is  necessary  to  take  the  value  of 
the  water  into  consideration.  In  this  connection,  it  should  be  borne 


DISTRIBUTION  SYSTEMS  113 

in  mind  that  water  for  irrigation  is  becoming  constantly  more  and 
more  valuable,  and  that  while  at  the  present  time  it  is  delivered 
through  inefficient  measuring  devices,  it  is  probable  that  within  a  few 
years,  on  account  of  the  increased  demands  for  water  for  irrigation 
purposes  and  its  correspondingly  increased  value,  careful  measure- 
ments will  be  required.  It  is  being  more  and  more  appreciated  that 
in  order  to  properly  regulate  the  amount  of  water  placed  upon  lands 
fairly  accurate  measurements  of  the  quantity  used  must  be  kept. 
Wherever  possible,  therefore,  as  accurate  means  of  measuring  as  are 
consistent  with  the  conditions  at  hand  should  be  provided. 

Flumes  and  Pipe  Distributaries. — In  many  irrigated  sections 
flumes  and  pipes  are  commonly  used  instead  of  earthen  channels  for 
the  smaller  distributaries.  The  principal  advantage  of  a  flume  or 
pipe  over  an  earthen  canal  is  the  saving  of  water.  They  are  also 
sometimes  used  on  rough  or  undulating  areas  to  avoid  fills  and  cuts 
which  would  be  necessary  in  constructing  the  small  earthen  channels. 
In  very  pervious  materials,  such,  for  example,  as  sand  and  gravel,  it 
is  impossible  to  carry  a  small  quantity  of  water  for  any  considerable 
distance  in  an  earthen  canal  on  account  of  the  rapid  absorption  of 
water  by  the  soil. 

The  smaller  the  quantity  of  water  carried,  in  pervious  materials, 
the  greater  is  the  relative  effect  of  losses  and  the  shorter  the  distance 
which  water  may  be  delivered.  For  example,  in  a  channel  carrying 
50  or  100  second-feet,  seepage  losses  which  may  amount  to  i 
or  2  second-feet  per  mile  may  be  neglected,  since  they  represent  but 
a  small  percentage  of  the  quantity  of  water  carried.  If,  however, 
a  channel  carrying  but  i  or  2  second-feet  has  the  same  rate  of  loss 
per  square  foot  of  wetted  area  in  its  channel,  the  entire  quanity  is 
soon  absorbed. 

Flume  or  pipe  distributaries  not  only  facilitate  the  flow  of  water 
and  make  irrigation  possible  on  lands  where  it  would  otherwise  be 
practically  impossible,  but  they  also  result  in  large  savings  of  water. 
These  savings  are  sufficient  in  many  cases  to  justify  a  large  original 
outlay  for  their  construction.  Pipes,  as  a  rule,  are  much  more 
satisfactory  than  flumes,  especially  in  warm  climates  where  it  is  not 
necessary  to  protect  them  from  freezing,  either  by  careful  drainage 
during  the  winter  or  by  burying  them  to  a  sufficient  depth  below  the 
frost  line. 

Wooden  flumes  are  frequently  used  to  cross  low  depressions, 
especially  in  the  northern  lands  where  lumber  is  relatively  cheap. 
Wooden  pipes  are  also  sometimes  used  for  this  same  purpose.  These 


114      PRINCIPLES  OF  IRRIGATION  ENGINEERING 

pipes  are  laid  so  as  to  act  as  inverted  siphons  under  a  small 
head. 

Cement  pipes  are  commonly  used  for  distributaries  in  the  inten- 
sively cultivated  sections  of  southern  California  where  the  water 
supply  is  limited  and  where  it  is  necessary  to  conserve  it  to  the  high- 
est possible  degree.  These  pipes  are  laid  to  a  sufficient  depth  to 
insure  their  protection  against  the  cultivation  of  the  soil  and  are 
provided  with  frequent  taps  carried  up  to  the  surface  from  which 
water  is  discharged.  They  are  constructed  sufficiently  strong  to 
carry  low  heads  and  serve  as  pressure  pipes  where  necessary  to  carry 
water  across  slight  depressions  in  the  ground.  With  a  distribution 
system  of  this  kind,  little  if  any  water  need  be  wasted  since  it  can  be 
distributed  from  the  pipes  only  at  such  points  as  required. 

Accessibility  to  Laterals. — In  designing  and  laying  out  a  distribu- 
tion system  provisions  must  be  made  for  easy  access  to  all  parts 
thereof.  It  must  be  borne  in  mind  that  even  for  the  smallest  canals 
which  form  a  part  of  a  system  for  the  delivery  of  \v  ater  they  must  be 
patrolled  and  operated  almost  daily.  It  is  consequently  of  the 
greatest  importance  that  the  person  in  charge  of  operation  and  main- 
tenance of  these  canals  be  unhampered  in  Ijds  efforts  to  reach  them 
for  this  purpose.  In  order  to  properly  maintain  laterals,  it  is 
necessary  that  materials  can  be  delivered  to  them  quickly  if  necessary. 
In  the  event  of  banks  being  broken  or  washed  away,  earth  for  the 
repairs  of  the  same  is  necessary,  and  provisions  must  be  made  for 
obtaining  this  material  without  delay. 

The  remarks  heretofore  made  relative  to  rights-of-way  for  canal 
apply  equally  well  to  the  smaller  distribution  canals,  and  no  canal, 
however  small,  which  is  to  form  an  integral  part  of  a  system  and  for 
which  the  owners  of  su'ch  system  are  responsible  for  its  maintenance, 
should  be  constructed  except  on  rights-of-way  under  their  control. 
It  matters  not  whether  these  rights-of-way  be  actually  owned  by  an 
irrigation  company  or  whether  the  right-of-way  for  the  canal  is 
simply  in  the  form  of  an  easement,  the  main  question  is  that  no  one 
shall  have  any  right  to  dispute  the  authority  of  the  operators  to 
enter  on  the  right-of-way  and  operate  and  maintain  canals  in  a  proper 
manner. 

Canal  systems  are  built  for  the  benefit  and  use  of  persons  engaged 
in  tilling  the  soil,  and  it  is  essential  that  these  persons  be  unhampered 
in  their  farming  operations  by  undue  restrictions  on  access  to  their 
canals.  This  is  especially  true  on  small  distribution  canals  which 
must  of  necessity  cross  irrigable  lands.  The  cooperation  of  both 


DISTRIBUTION  SYSTEMS  115 

the  water  users  and  the  company  or  firm  delivering  the  water  is 
necessary.  In  order  that  this  cooperation  shall  be  effective,  con- 
cessions must  frequently  be  made  by  both  parties,  and  any  agree- 
ments for  rights-of-way  should  be  made  specific  enough  to  fully 
define  the  rights  of  each. 

Conditions  frequently  arise  where  a  small  distribution  canal  must 
be  constructed  across  private  holdings  in  order  to  supply  water  to 
the  lands  of  others.  Such  a  canal  is  often  a  detriment  to  the  person 
whose  lands  it  crosses  and  may  be  unnecessary  for  his  individual  use. 
In  such  cases,  it  is  absolutely  necessary  that  no  opportunity  be  given 
to  this  owner,  should  he  be  so  inclined,  to  interfere  with  the  delivery 
of  water  to  the  irrigators  below.  Right-of-way  agreements  in  such 
a  case  should  be  so  specific  that  it  is  not  left  to  one  individual  to  say 
whether  or  not  his  neighbor  shall  receive  water. 

The  amount  of  right-of-way  which  will  be  required  in  individual 
cases,  will,  of  course,  depend  upon  local  conditions.  It  is  essential, 
however,  that  in  every  case  there  be  sufficient  to  permit  the  canals 
to  be  operated  and  allow  repairs  to  be  made  promptly  when  neces- 
sary. In  general,  it  may  be  said  that  the  rights  of  the  people  under 
a  distribution  system  are  paramount  to  the  rights  of  any  one  indi- 
vidual, since  it  is  only  upon  this  basis  that  an  irrigation  system  can  be 
made  a  success.  In  other  words,  the  individual  cannot  be  allowed  to 
retard  the  work  of  others  on  account  of  inconveniences  to  himself. 

On  the  other  hand,  the  individual,  where  land  is  crossed  by  a  canal, 
or  lateral,  is  entitled  to  the  protection  in  his  rights  and  conveniences 
consistent  with  the  rights  of  the  people  as  a  whole  under  canals. 
For  example,  the  individual  whose  land  is  thus  traversed  is  unques- 
tionably entitled  to  bridge  crossings  which  will  give  him  free  access 
to  his  land.  Provisions  must  also  be  made  for  these  crossings 
being  maintained  in  such  a  manner  that  they  will  not  interfere  with 
the  operation  of  the  canal.  The  person  or  company  responsible 
for  the  operation  of  the  canal  system  must  have  access  to  all  parts 
of  that  system.  Such  right  of  access,  however,  should  not  give 
them  the  right  to  unnecessarily  inconvenience  adjacent  land  owners. 

It  is  impossible  to  lay  down  any  hard  or  fixed  rules  as  to  exactly 
what  should  be  acquired  in  the  way  of  rights-of-way.  Each 
particular  case  must  be  given  due  consideration  in  the  planning  of 
a  distributon  system  and  rights-of-way'  acquired  so  as  to  fully 
protect  the  interests  of  the  individual  whose  lands  are  crossed,  and 
also  provide  for  the  carrying  on  of  operation  and  maintenance  work 
in  such  manner  as  to  make  the  system  fully  effective. 


CHAPTER  VII 

» 

IRRIGATION  BY  PUMPING 

General  Conditions. — It  frequently  becomes  necessary  for  the 
engineer  to  consider  the  practicability  of  supplying  water  for  irriga- 
tion by  pumping.  Conditions  of  this  kind  may  be  the  result  of  the 
lands  being  situated  at  a  higher  elevation  than  any  available  water 
supply,  thus  making  irrigation  by  gravity  impossible,  or  it  may  be 
that  the  distance  from  a  gravity  supply  is  too  great  or  the  character 
of  the  country  such  as  to  make  the  building  of  canals  impracticable. 

The  general  principles  involved  in  pumping  for  irrigation  are  not 
unlike  those  involved  in  pumping  for  municipal  and  domestic  uses. 
Concerning  the  latter  there  are  many  data  available  which  may 
have  general  application  to  pumping  for  irrigation.  It  must  be 
recognized,  however,  that  the  quantity  of  water  required  for  irriga- 
tion ordinarily  greatly  exceeds  that  needed  for  a  municipal  and  do- 
mestic supply.  Another  important  point  to  be  considered  is  the 
value  of  water  for  irrigation  purposes  compared  to  what  it  is  worth 
for  the  use  of  a  town  or  city.  A  price  which  'may  be  considered 
reasonable  and  which  the  residents  of  a  town  can  well  afford  to  pay 
for  domestic  use  may  be  excessive  when  considered  in  connection 
with  agricultural  operations.  This  is  because  of  the  fact  that  the 
amount  of  water  required  for  irrigation,  considered  with  reference 
to  cost,  is  excessive  when  compared  with  that  necessary  for  all  pur- 
poses in  cities  of  moderate  size. 

The  pumping  equipment  which  would  be  well  within  the  financial 
means  of  a  city  covering  a  thousand  acres  would  be  no  more  than 
adequate  for  a  farm  of  the  same  extent.  The  return  in  revenue, 
however,  between  these  two  areas,  one  covered  by  business  blocks 
and  residences,  is  many  times  that  which  would  be  received  from 
profits  derived  from  the  sale  of  crops  grown  on  an  equal  extent  of 
land. 

Thus  a  pumping  plant  which  might  be  of  relatively  low  cost  when 
considered  for  the  city,  is  out  of  the  question  for  the  country. 

The  fundamental  differences  which  must  be  considered  in  study- 
ing successful  pumping  plants  installed  for  municipal  purposes  and 
in  adopting  similar  plants  for  agricultural  purposes  lie  in  the  follow- 
ing facts: 

116 


IRRIGATION  BY  PUMPING  117 

For  city  purposes  a  relatively  small  quantity  of  water  is  required 
to  be  lifted  to  a  considerable  height,  in  many  cases  200  ft.  or  more, 
while  for  ordinary  irrigation  purposes  70  ft.  is  at  present  near  the 
maximum.  The  quantity  of  water  for  city  purposes  is  expressed 
in  gallons  per  minute;  that  for  agricultural  purposes  in  cubic  feet 
per  second,  i  cu.  ft.  per  second  equaling  449  gal.  per  minute.  The 
total  quantity  pumped  is  expressed  for  city  purposes  in  millions  of 
gallons;  for  agricultural  purposes  in  acre-feet;  i  acre-foot  equaling 
325,850  gallons,  or  about  a  third  of  a  million  gallons;  and  one  million 
gallons  equaling  3.07  acre-feet. 

The  cost  of  raising  water  for  a  city  may  be  as  high  as  $20  to  $30 
per  million  gallons,  or  about  $6  to  $10  per  acre-foot,  while  for  ordi- 
nary field  crops  a  fair  cost  would  be  50  cents  per  acre-foot,  and 
a  large  cost  $i  per  acre-foot. 

For  city  purposes  the  supply  must  be  practically  continuous  day 
and  night,  increasing  during  the  extreme  heat  of  the  summer  when 
water  is  used  for  irrigating  lawns  and  gardens  or  similar  small  areas. 
Thus  the  men  and  machinery  are  kept  continuously  employed. 

For  agricultural  purposes  a  supply  is  ordinarily  required  for  a  few 
months  only  during  the  irrigation  season.  Even  during  this  period 
the  amount  required  is  by  no  means  constant.  For  a  short  time 
during  the  early  heat  of  summer  the  demand  is  large,  but  drops  off 
rapidly  as  cooler  weather  approaches.  Thus  it  happens  that  men 
and  machinery  employed  in  pumping  for  irrigation  are  idle  for  a 
large  part  of  the  time  unless  some  secondary  employment  can  be 
found  for  them. 

Source  of  Supply. — -A  well  of  some  form  may  be  considered 
as  the  typical  source  of  supply  of  water  pumped  for  agriculture. 
Conditions  may  arise  where  it  is  possible  to  pump  water  from  a 
flowing  stream.  As  a  rule  such  stream  is  of  large  size  and  has  such 
gentle  slopes  that  it  cannot  be  diverted  by  gravity,  otherwise  pumps 
would  not  be  used.  Under  some  conditions  water  may  be  pumped 
from  a  lake  or  possibly  from  a  canal.  It  is  usually  desirable,  how- 
ever, even  in  the  case  of  a  river  or  lake,  to  provide  some  form  of 
forebay,  which  is  practically  a  well  built  on  the  side  of  a  stream 
or  lake  and  connected  with  it  so  that  the  water  in  the  well  rises 
or  falls  with  the  fluctuations  in  the  river  or  lake.  Wells  of  this 
character,  fluctuating  within  a  narrow  range,  present  fewer  prob- 
lems than  the  ordinary  form  of  dug  or  driven  well  since  the  water 
in  the  former  usually  fluctuate  less  in  height  and  thus  offer  fewer 
problems  in  the  design  cf  economical  machinery. 


118      PRINCIPLES  OF  IRRIGATION  ENGINEERING 

Having  determined  that  the  available  source  of  water  supply 
must  be  utilized  by  pumping,  the  next  condition  to  be  considered  is 
the  fluctuation  in  the  height  of  water  and  the  variation  in  amount, 
these  being  usually  interrelated.  If  the  source  is  a  large  stream 
or  lake,  the  questions  connected  with  quantity  become  insignificant 
and  those  of  the  amount  of  rise  and  fall  of  water  surface  are  of 
more  importance.  In  the  case  of  ordinary  wells  in  earth,  however, 
the  question  of  quantity  or  rate  of  delivery  to  the  well  become 
paramount,  controlling  as  it  does  not  only  the  height  of  water  in  the 
well,  but  the  size  and  other  conditions  of  the  machinery  to  be  used. 

Observations  of  the  height  and  fluctuation  of  the  source  of  water 
carried  on  through  several  months  or  years  are  essential  in  preparing 
designs  for  a  pumping  plant.  Every  possible  information  as  to 
the  hydrographic  conditions  should  be  studied.  If  it  is  a  matter 
of  general  knowledge  that  the  lake  or  river  under  consideration 
has  fluctuated  within  a  certain  range  for  many  years  these  questions 
may  be  considered  as  settled.  In  the  case  of  ordinary  dug  or  drilled 
wells,  however,  the  question  of  quantity  of  water  is  far  more  difficult 
of  solution.  Frequently  it  is  impossible  to  give  such  wells  a  thorough 
test  in  advance  because  the  cost  of  erecting  testing  devices — con- 
sisting of  machinery  of  sufficient  capacity  to  thoroughly  exhaust 
the  wells — may  be  practically  as  expensive  as  to  build  the  final 
plant.  The  only  tests  which  have  real  value  are  those  which  are 
made  through  days,  weeks  or  months  to  determine  as  thoroughly 
as  possible  all  local  conditions  of  rate  of  flow  to  the  well,  for  this 
purpose  drawing  down  the  stored  water  accumulated  in  the  strata 
in  the  immediate  vicinity. 

There  are  many  popular  fallacies  concerning  the  amount  of 
water  under  ground,  especially  as  regards  the  "  inexhaustible " 
supply.  The  use  of  the  word  "inexhaustible"  in  this  connection 
usually  implies  that  with  the  ordinary  hand  pump  or  similar  devices 
it  has  not  been  possible  to  appreciably  lower  the  surface  of  the 
ground  water.  Another  term  which  has  come  into  general  use  in 
the  west,  especially  in  the  region  of  the  Great  Plains,  and  which 
conveys  erroneous  impressions,  is  the  word  "underflow."  There 
is,  it  is  true,  an  underflow  but  the  rate  of  this  is  exceedingly  slow, 
and  a  more  descriptive  term  would  be  "percolation."  The  word 
"flow"  in  the  minds  of  most  people  is  connected  with  the  behavior 
of  a  river  moving  at  a  rate  perceptible  to  the  eye,  such  as  a  mile 
or  two  an  hour.  The  "underflow,"  if  it  can  be  said  to  flow  at  all, 
moves  at  the  rate  of  from  i  to  5  ft.  a  day,  or  possibly  at  a  slightly 


IRRIGA TION  BY  P UMPING  119 

more  rapid  rate  when  in  coarse  sand  or  gravel.  The  assumption 
occasionally  made  in  popular  literature  that  there  is  under  ground 
a  great  river  moving  steadily  forward  and  carrying  more  water 
than  there  is  in  sight  on  the  surface  is  a  fanciful  rather  than  an 
actual  condition.  In  western  Kansas,  for  example,  it  is  popularly 
stated  that  the  Arkansas  River  carries  more  water  underground 
out  of  sight  than  in  the  visible  surface  channel.  A  little  reflection 
will  show  that  this  cannot  be  true. 

Careful  tests  have  been  made  to  show  the  existence  of  this  under- 
flow and  to  secure  measurements  of  the  rate  and  direction  of  move- 
ment. This  is  done  by  putting  down  a  series  of  wells  in  lines  or 
groups  and  impregnating  the  waters  of  one  of  these  wells  with 
ordinary  table  salt  or  some  other  soluble  material,  the  presence  of 
which  can  be  detected  by  electric  or  mechanical  devices.  It  has 
been  discovered  that  there  is  a  definite  forward  movement  of  the 
waters  percolating  through  the  sands  and  gravels  which  underlie 
the  Valley  of  the  Arkansas  River,  and  that  the  surface  configuration 
does  not  necessarily  indicate  the  size  or  extent  of  these  deeper  beds 
in  which  water  is  progressing  southerly  or  southeasterly  in  a  diagonal 
line  across  the  present  river  channel. 

These  beds  of  pervious  material  are  very  large  and  their  cross- 
sectional  area  is  probably  many  times  greater  than  the  cross-section 
of  the  surface  stream,  but  the  extremely  slow  rate  of  movement 
of  a  few  feet  a  day  as  compared  with  2  or  3  ft.  per  second  on  the 
surface,  results  in  there  being  a  relatively  small  amount  of  water 
per  annum  carried  through  these  sand  and  gravel  bsds. 

There  is  little  doubt  that  the  ground  water  is  reinforced  to  a 
certain  extent  by  this  slow,  gradual  percolation,  especially  through 
widely  spread  sands  and  gravels,  but  this  rate  of  flow  is  rarely  suffi- 
cient to  maintain  the  water  table  at  the  original  height  in  any  country 
where  wells  have  been  in  use  to  a  notable  extent.  McGee1  has  pointed 
out  that  in  all  settled  parts  of  the  United  States  there  has  been  a 
decided  lowering  of  the  water  table,  especially  where  the  ordinary 
dug  wells  have  been  supplemented  by  a  large  number  of  the  cheaper 
and  deeper  drilled  or  driven  wells.  He  has  also  shown  that  in  spite 
of  wet  years  the  water  table  does  not  return  permanently  to  its  former 
height.  If  this  is  true  for  regions  where  the  demand  for  water  from 
underground  is  limited  chiefly  to  domestic  supply  or  for  the  watering 
of  cattle,  the  effect  must  be  more  marked  where  considerable  num- 
bers of  wells  are  provided  for  irrigation  of  the  surface,  as  the  amount 

i  Wells  and  Subsoil  Waters,  by  W.  S.  McGee,  U.  S.  Dept.  Agriculture,  Bureau  of  Soils, 
Bulletin  No.  92. 


120      PRINCIPLES  OF  IRRIGATION  ENGINEERING 

of  water  pumped  from  these  for  agriculture  greatly  exceeds  that 
which  is  needed  for  domestic  purposes. 

In  constructing  a  well  where  the  ground  waters  are  apparently 
abundant,  it  is  desirable  to  sink  a  caisson  from  the  surface  into  the 
water  plane  as  far  as  it  can  be  driven,  using  a  pump  having  a  capacity 
twice  that  of  the  pump  finally  installed.  When  this  is  done,  it  is 
usual  to  drill  in  the  bottom  of  this  caisson  two  or  more  of  the  so- 
called  California  wells  and  connect  suction  pipes  to  the  pump 
extending  down  into  these  driven  wells.  Normally  these  pumps  will 
draw  water  from  the  wells  and  from  the  bottom  of  the  caisson  in 
which  they  terminate.  If  the  water  plane  is  drawn  down  it  will  then 
be  possible  to  secure  water  from  the  wells  even  if  the  bottom  of  the 
caisson  becomes  dry.  If  the  pump  loses  its  suction  from  any  cause 
the  water  plane  will  rise  until  the  pump  is  submerged  and  again 
put  in  operation.  As  an  alternative  method,  but  one  which  is  not 
usually  to  be  recommended,  is  that  of  driving  small  tunnels  to 
connect  wells  situated  outside  the  caisson.  A  well  made  by  sinking 
a  caisson  to  some  distance  below  the  surface  of  the  underground 
waters,  and  having  its  depth  still  further  increased  by  drilled  wells 
in  the  bottom  of  the  caisson,  is  considered  the  most  permanent  form 
of  construction  that  can  be  adopted. 

Character  of  Pumps. — The  pumps  first  used  in  irrigation  were 
naturally  those  which  previously  had  been  found  successful  for 
pumping  town  supplies,  namely,  those  with  plungers  or  pistons. 
They  fall  into  two  classes — first,  those  placed  horizontally  with 
suction  lift  and  requiring  a  certain  amount  of  horizontal  space  for 
installation,  and  second,  the  vertical  acting  pumps  usually  so  small 
in  horizontal  diameter  that  they  can  be  inserted  directly  into  the  well 
and  are  thus  frequently  submerged,  attaining,  as  a  rule,  greater  effi- 
ciency because  of  this  condition.  These  pumps  were  all  of  the  re- 
ciprocating type,  not  well  suited  for  economically  delivering  large 
quantities  of  water  such  as  are  required  in  irrigation.  They  have 
for  this  reason  been  supplemented  in  modern  practice  by  centrifugal 
pumps  of  the  single-stage  type  for  moderately  low  heads  and  the  mul- 
tiple-stage type  for  high  heads. 

A  form  of  centrifugal  pump  largely  used  and  operated  by  electrical 
power  for  irrigation  is  one  in  which  the  pump  and  motor  driving 
it  are  mounted  on  the  same  vertical  shaft,  frequently  they  are  ar- 
ranged in  such  way  that  the  pump  and  motor  can  be  raised  and  low- 
ered as  a  unit.  It  is  not  practicable  to  mount  the  motor  immediately 
above  the  pump  because  the  fluctuations  of  water  in  the  well  are 


IRRIGATION  BY  PUMPING  121 

usually  so  great  that  the  motor  would  be  in  danger  of  being  sub- 
merged and  thus  injured.  It  is  necessary,  therefore,  that  the  verti- 
cal shaft  be  of  sufficient  length  to  permit  submergence  of  the  pump 
and  at  the  same  time  keep  the  motor  well  above  the  water  level. 
This  is  accomplished  by  providing  a  light,  steel  frame  on  the  upper 
end  of  which  is  carried  the  motor,  and  on  the  lower  end  the  pump,, 
the  connecting  shaft  being  supported  by  the  frame  at  intermediate 
points  so  that  the  whole  device  forms  a  stiff  but  relatively  light  unit, 
which  can  be  hung  or  supported  in  a  well  and,  if  necessary,  adjusted 
to  different  heights  to  suit  the  elevation  of  water  in  the  well. 

The  pump  frame  may  be  of  galvanized  structural  steel,  or  iron, 
or  of  wood,  and  be  suspended  from  beams  placed  across  the  top  of 
the  casing  of  the  well,  the  internal  diameter  of  which  should  be 
ample  to  permit  insertion  of  the  discharge  pipe  and  the  raising  and 
lowering  of  the  pump  as  shown  in  Fig.  34. 

The  pump  is  usually  placed  at  a  depth  of  from  30  to  50  ft.  below 
the  surface  of  the  ground  and  a  discharge  pipe  is  carried  up  vertically 
to  the  surface  independent  of  the  frame.  The  adjustment  is  made 
so  as  to  submerge  the  pump  in  such  a  position  that  the  water  surface 
may  rise  15  or  20  ft.  or  more  above  the  pump  and  fall  possibly 
10  or  15  ft.  below  it. 

The  capacity  of  centrifugal  pumps  arranged  for  irrigation  should 
be  selected  to  suit  the  varying  conditions  of  head  and  available 
water  supply.  In  this  manner  a  high  degree  of  efficiency  can  be 
obtained  under  all  conditions,  with  the  simplest  form  of  automatic- 
ally operated  constant-speed  apparatus.  The  maximum  head 
which  is  practicable  for  the  ordinary  single-stage  centrifugal  pump 
is  about  60  ft.  Multiple-stage  pumps  may  be  used  for  any  head 
desired.  A  modified  form  of  the  multi-stage  centrifugal  pump 
known  as  the  deepwell  turbine  pump  may  be  assembled  in  two 
or  more  units  of  such  dimensions  that  the  pump  with  its  discharge 
pipe  and  self-contained  shaft  can  be  installed  in  a  driven  well  casing 
and  driven  by  either  a  belt  or  motor. 

Power  for  Pumping. — Nearly  every  kind  of  power  from  the  strength 
of  animals,  probably  the  earliest  form,  to  the  most  modern  hydro- 
electrical  systems  of  development  and  transmission,  has  been  used 
for  pumping  water  for  irrigation.  At  the  present  day  it  is  not 
necessary  to  consider  the  use  of  animal  power,  although  in  a  few 
instances  under  pioneer  conditions  or  for  testing  the  supply,  vari- 
ous forms  of  machinery  operated  by  horses  may  be  temporarily 
employed. 


122      PRINCIPLES  OF  IRRIGATION  ENGINEERING 


FIG.  34. — Vertical  section  of  concrete  lined  well  shaft,  with  electrically  driven 
centrifugal  pump,  Salt  River  Project,    Arizona. 


IRRIGATION  BY  PUMPING  123 

Windmills. — Next  in  order  historically,  and  naturally  to  the 
strength  of  men  and  animals,  comes  the  use  of  wind.  This  is  still 
quite  largely  employed  for  irrigating  small  tracts  of  ground.  (See 
U.  S.  G.  S.  Water  Supply  Papers  No.  i,  8,  20,  29,  41,  and  42.) 
Windmills  have  been  improved  during  recent  years,  adapted  to 
various  purposes  and  are  now  a  commercial  article  readily  obtainable 
through  agricultural  implement  dealers.  In  considering  the  use 
of  wind  as  a  source  of  power,  it  is  necessary  mainly  to  secure  a  good 
commercial  mill,  using  certain  precautions,  however,  in  estimating 
.the  actual  available  power,  due  allowance  being  made  for  assump- 
tions, based  on  ideal  conditions. 

It  is  usually  necessary  to  supplement  any  form  of  wind-mill 
pump  with  adequate  water  storage  because  of  the  fact  that  the 
amount  of  water  lifted  is  relatively  very  small,  and  with  the  uncer- 
tainty of  the  wind,  this  small  stream  of  water  coming  at  irregular 
intervals  will  soak  into  the  ground  before  it  can  be  beneficially 
used  in  irrigation.  The  necessity  of  a  storage  tank  arises  from  the 
fact  that  in  order  to  carry  the  water  rapidly  and  effectively  over 
the  ground,  it  is  necessary  to  have  a  considerable  volume  or  head, 
such  that  the  water  will  pass  over  or  across  porous  soils  so  rapidly 
that  no  very  considerable  portion  can  be  lost  in  transit.  (See  Plate 
IX,  Figs.  A  and  B.) 

The  cost  of  irrigation  by  windmills  is  generally  prohibitory 
excepting  for  intensively  cultivated  market  gardens.  It  is  rarely 
possible  to  irrigate  more  than  one-half  or  three-fourths  of  an  acre 
with  a  windmill,  unless  the  mill  is  unusually  large,  and  the  lift 
very  low.  The  cost  for  irrigation  including  construction  of  well, 
purchase  of  windmill,  pump,  construction  of  tank,  and  accessories, 
may  amount  to  from  $100  to  $500  an  acre.  The  cost  of  maintenance 
is  correspondingly  large,  as  all  forms  of  windmill  require  frequent 
attention  and  more  or  less  repairs.  The  deterioration  also  is  usually 
quite  heavy  so  that  the  annual  maintenance  cost  of  the  equipment 
rarely  falls  below  $10  or  $20  per  acre,  if  allowance  is  made  for  the 
time  spent  in  keeping  the  apparatus  in  order. 

Steam  Power. — One  of  the  commonly  applied  forms  of  power 
for  pumping  is  steam  generated  by  burning  coal  or  sometimes  oil 
in  the  ordinary  steam  boilers,  utilizing  the  force  of  the  steam  in 
reciprocating  engines  which  drive  suitable  pumps  by  means  of 
belt  or  gear  connections  or  by  direct  piston  connection.  When 
used  in  irrigation  the  apparatus  is  sometimes  an  adaptation  of 
the  steam  pumps  used  for  town  supply.  Where  the  crops  are  very 


124      PRINCIPLES  OF  IRRIGATION  ENGINEERING 

valuable,  as  in  the  case  of  sugar-cane  in  the  Hawaiian  Islands, 
steam  pumps  are  used  with  success  in  agriculture,  raising  water 
100  or  more  feet  in  height,  the  extreme  limit  being  estimated  at 
about  550  ft.  The  acreage  cost  for  installation  is,  of  course, 
exceedingly  high,  over  $100  an  acre  at  the  minimum,  and  the  annual 
maintenance  and  operation  cost  for  high  lifts  may  run  from  $30 
to  $50  per  acre.  The  cost  is  thus  prohibitory  for  ordinary  crops, 
unless  some  unusual  conditions  exist. 

Steam  turbines  have  been  employed  in  place  of  reciprocating 
engines,  these  being  connected,  as  a  rule,  to  electrical  generators, 
which  in  turn  operate  motors  to  drive  the  pumps.  A  relatively 
high  degree  of  efficiency  has  thus  been  secured  and  the  size  and 
consequent  cost  of  installation  has  been  notably  reduced  below  that 
of  the  other  devices.  Especially  is  this  true  where  a  large  quantity 
is  to  be  pumped,  and  where  several  pumping  units  can  be  supplied 
with  power  from  one  central  station. 

Gasoline  and  Oil. — A  steam  plant  for  pumping  water  for  irrigation 
necessitates,  for  fuel  economy,  large  investment  and  the  irrigation  of 
considerable  areas,  more  extensive  usually  than  can  be  handled  by 
an  individual.  There  has  thus  arisen  a  demand  for  small  individual 
pumping  plants  to  irrigate  from  40  to  80  acres,  or  more.  For  this 
purpose  the  ordinary  gasoline  or  gas  engines  have  been  found  very 
effective.  Such  engines  may  be  considered  as  replacing  or  supple- 
menting the  windmill.  They  permit  a  control  of  the  water  supply 
such  as  cannot  be  had  by  dependence  upon  the  wind  and  at  the 
same  time  they  can  be  of  such  size  and  capacity  as  to  be  within  the 
reach  of  the  individual  farmer. 

Pumping  plants  of  this  character  have  been  installed  at  a  first  cost 
of  from  $50  to  $100  per  acre,  and  upward.  The  cost  of  operation 
and  maintenance  per  acre  is  usually  larger  than  that  of  the  windmill 
and  compares  favorably  with  that  of  the  steam  engine  but  is  higher 
than  from  gravity  sources,  ranging  from  $5  to  $10  per  acre.  These 
forms  of  engines  are  undergoing  rapid  improvement  and  develop- 
ment, so  that  the  engineer  in  considering  the  practicability  of  install- 
ing machinery  of  this  kind  should  be  advised  of  the  most  recent 
experience  in  order  not  to  repeat  the  errors  of  his  predecessors. 

The  gasoline  engine  using  distillate  is  reported  to  be  doing  about 
80  per  cent,  of  that  part  of  the  pumping  in  southern  California  which 
is  not  being  done  by  electric  power — thus  indicating  a  considerable 
advantage  over  the  steam  engine.  These  distillate  engines  use  the 
cruder  distillate  from  petroleum  and  are  built  up  to  as  high  as  300 


PLATE  IX 


FIG.  A. — Pumping  water  by  wind  mill  into  earth  tank  from  which  an  irrigating 
stream  can  be  drawn. 


FIG.  B. — Gasoline  pumping  equipment,  delivering  water  into  small  earth 

reservoirs. 

(Facing  Page  124.) 


FIG.   C. — Generators  driven  by  water  power  furnishing  electrical  energy  for 
pumps.     Minidoka  Project,  Idaho. 


FIG.  D. — Electrically  operated  centrifugal  pumps  delivering  water  to  laterals  on 
Gila  River  Indian  Reservation,  Ariz. 


IRRIGATION  BY  PUMPING  125 

h.p.,  thus  irrigating  large  tracts  of  lands.  Although  the  large 
distillate  engine  which  requires  the  services  of  an  engineer  is  not  as 
economical  as  a  high-grade  steam  plant  using  the  cruder  unrefined 
oils,  yet  as  the  irrigation  of  much  of  the  country  is  subject  to  inter- 
ruption, the  lower  first  cost  of  the  plant  and  the  short  time  it  is  used 
offsets  the  higher  fuel  cost. 

Many  of  the  owners  of  orchards  in  southern  California  are  supply- 
ing themselves  and  neighbors  with  water  by  engines  which  are  not 
visited  sometimes  more  than  twice  in  a  day's  run  of  ten  hours.  The 
engines  are  reliable  and  fairly  economical,  if  ordinary  attention  is 
given  them.  A  still  higher  economy  may  be  obtained  when  there 
are  introduced  various  forms  of  producer  gas  from  either  oil  or  coal. 

Water  Power. — The  use  of  water  power  is,  theoretically  at  least, 
the  most  economical  of  methods  for  pumping  water.  Usually  it  is 
considered  in  connection  with  development  of  electricity  and  the 
transmission  of  power  to  points  where  the  pumps  are  to  be  operated, 
forming  thus  a  hydroelectric  combination.  There  are  cases,  how- 
ever, where  it  is  advisable  to  install  a  water-power  development  at 
the  point  where  the  water  is  to  be  pumped.  For  example,  on  a  main 
canal  the  topography  of  the  ground  may  be  such  as  to  necessitate  or 
make  desirable  the  putting  in  of  a  drop  in  the  bed  of  the  canal. 
Power  can  be  developed  at  this  drop  to  lift  a  portion  of  the  water 
to  the  lands  above  the  level  of  the  main  canal.  Automatic  pumps 
for  this  purpose  have  been  devised  and  successfully  operated  at 
relatively  small  expense,  such  for  example  in  connection  with  the 
Huntley  Montana  Reclamation  project,  where,  with  the  drop  of 
30  ft.  in  the  main  canal,  a  portion  of  the  water  is  lifted  to  a  height  of 
50  ft.  above  the  canal  to  irrigate  higher  lands  as  shown  in  Fig.  35. 

The  device  used  at  Huntley  consists  of  a  turbine  wheel  attached  to 
the  lower  end  of  the  vertical  shaft  on  the  upper  end  of  which  is  a 
centrifugal  pump,  the  water  passing  into  the  turbine  wheel  actuates 
it,  driving  the  centrifugal  pump  which  in  turn  is  fed  by  a  portion  of 
the  water  which  is  flowing  toward  the  turbine.  This  portion,  about 
one- third  of  the  capacity  of  the  penstock,  is  forced  upward  to  a  higher 
level. 

This  machine  is  enclosed  within  a  cylindrical  case,  so  that  all  parts 
of  the  machinery  are  protected  and  when  once  installed  the  pump 
runs  continuously  with  a  minimum  of  attention  throughout  the 
irrigation  season. 

Hydraulic  rams  can  also  be  installed  in  localities  of  this  kind,  this 
device  depending  upon  the  water  hammer  or  ram  of  the  water, 


126      PRINCIPLES  OF  IRRIGATION  ENGINEERING 


I 

I 


IRRIGATION  BY  PUMPING  127 

which  when  falling  rapidly  is  suddenly  checked,  the  momentum 
causing  a  portion  of  the  water  to  be  forced  to  a  higher  elevation. 
These  rams  have  reached  a  capacity  as  high  as  5  cu.  ft.  per  second 
of  delivery,  and  are  found  to  be  very  economical  for  installation. 
They  are  very  noisy  and  the  shock  of  the  arm  rapidly  wears  the 
moving  parts  unless  these  are  carefully  adjusted.  They  are  easily 
clogged  or  put  out  of  order  and  on  the  whole  have  not  given  a  high 
degree  of  efficiency  for  continuous  operation  for  any  considerable 
period  of  time. 

Compressed  Air. — Where  compressed  air  can  be  readily  obtained 
from  an  established  plant,  it  has  been  found  feasible  to  lift  water  from 
deep  tubular  wells  by  means  of  what  is  known  as  the  air  lift.  For 
example,  in  the  vicinity  of  sugar-beet  factories  or  large  mills  where 
there  is  an  excess  of  power  or  of  compressed  air,  during  certain  parts 
of  the  year  arrangements  have  been  made  for  utilizing  the  air  for 
lifting  water  for  irrigation.  The  device  consists  essentially  of  an 
arrangement  of  vertical  pipes  by  which  compressed  air  is  carried  by 
means  of  a  small  pipe  to  near  the  bottom  of  the  well  casing,  and  there 
released.  The  air  ascending  through  the  water  confined  in  the  larger 
pipe  forming  the  well  tends  to  lift  the  water,  causing  it  to  overflow 
the  top  of  the  pipe.  The  advantages  claimed  are  a  large  capacity, 
low  maintenance  cost,  especially  in  sandy  water  which  cuts  the  valves 
of  mechanical  pumps,  and  low  operating  cost,  particularly  where  an 
air  compressor  is  readily  available.  The  disadvantages  lie  in  the  low 
efficiency,  the  relatively  great  depth  required,  as  the  air  pump  cannot 
be  used  in  a  shallow  well  or  reservoir,  and  the  impracticability  of 
using  highly  inclined  or  horizontal  course  for  the  water. 

The  efficiencies  as  measured  by  various  experimenters  generally  run 
from  about  25  to  33  per  cent.,  being  higher  in  some  laboratory  experi- 
ments, but  lower  in  actual  practice.  A  comparison  between  the 
efficiency  of  wells  pumped  with  air  lift  and  deep  steam  pumps  at 
Waukesha,  Wisconsin,  showed  an  efficiency  of  16  to  18  per  cent,  for 
air  lift  based  on  the  indicated  horse-power  in  the  steam  cylinder,  and 
an  efficiency  of  nearly  75  per  cent,  for  deep  well  pumps.  (See 
Bulletin  450,  University  of  Wisconsin,  Oct.,  1911.) 

Hydroelectrical  Power. — The  use  of  power  transmitted  by 
electricity  in  pumping  water  for  irrigation  or  the  hydroelectric  plant 
from  an  economic  or  engineering  standpoint,  is  one  of  the  ideal  com- 
binations of  mechanical  completeness  and  efficiency.  Like  most 
ideals,  it  is  yet  to  be  worked  out  completely,  although  the  results 
already  attained  demonstrate  the  great  possibilities.  It  occasionally 


128      PRINCIPLES  OF  IRRIGATION  ENGINEERING 

happens  that  in  planning  an  irrigation  system,  there  is  necessarily 
involved  a  drop  of  water  from  the  point  of  storage  back  into  the  river 
or  canal,  or  at  some  point  along  the  main  conduits. 

Occasionally  falls  of  water  on  the  canal  lines  occur  at  points  where 
direct  pumping  is  not  possible  but  where  water-wheels  may  be  in- 
stalled, power  developed  and  transmitted  for  the  operation  of  pumps 
placed  more  conveniently  to  the  irrigable  lands.  Under  such  con- 
ditions, the  engineer  should  plan  for  the  conservation  of  this  power 
and  prepare  estimates  as  to  the  practicability  of  utilizing  the  power 
in  bringing  the  water  to  the  lands  which  otherwise  could  not  be 
reached. 

As  an  example  of  one  of  the  recently  developed  hydroelectric 
plants  built  primarily  for  pumping  water  for  irrigation  is  the  station 
of  the  Minidoka  project  in  southern  Idaho,  a  plan  and  section  of 
which  are  given  in  Fig.  36.  A  view  of  the  interior  of  the  power 
house  is  shown  on  Plate  IX,  Fig.  C.  This  is  located  at  the  rock- 
fill  dam  across  Snake  River  near  Minidoka.  This  dam  has  a  height 
of  86  ft.  with  length  of  rock-fill  of  736  ft.  and  contains  242,500 
cu.  yd.  of  material.  (See  Plate  XV,  Fig.  A.)  It  raises  the  water 
surface  about  40  ft.  forming  a  body  of  water  known  as  Lake  Wal- 
cott.  A  certain  amount  of  water  claimed  by  prior  appropria- 
tors  must  pass  through  this  dam  for  use  at  points  below.  In  so 
doing  power  is  developed  for  use  in  pumping  water  to  the  lands 
lying  above  the  reach  of  gravity  water  from  Lake  Walcott. 

The  excess  power,  especially  that  obtained  during  the  non-irri- 
gating months  is  used  for  furnishing  heat,  light,  and  current  to  the 
towns  on  the  project.  Seven  thousand  kilowatts  are  generated  in 
five  separate  units,  and  transmitted  about  13  miles  at  33,000  volts 
to  three  pumping  stations.  The  first  lifts  about  650  cu.  ft.  per 
second  to  a  height  of  31  ft.  above  the  gravity  canal;  at  this  level 
about  10,000  acres  are  irrigated.  The  balance  of  the  water  is 
pumped  to  an  elevation  of  31  ft.  where  another  canal  irrigates 
about  15,000  acres.  The  remainder  of  the  water  is  pumped  an 
additional  31  ft.  to  the  highest  level,  from  which  about  23,000 
acres  are  irrigated.  The  building  shown  in  Fig.  36  is  located  on 
the  down-stream  side  of  the  concrete  controlling  works  across  Snake 
River.  The  building  is  of  reinforced  concrete  and  consists  of  a 
turbine  floor  and  generator  floor  and  galleries  as  shown  in  Plate 
IX,  Fig.  C.  The  building  is  150  ft.  long,  50  ft.  wide,  and  85 
ft.  high  on  the  down-stream  side.  The  turbines  when  fully  loaded 
are  rated  at  2,000  h.p.,  and  use  425  second-feet  of  water  under 


IRRIGATION  BY  PUMPING  129 

the  normal  head.  The  main  electric  units  are  i,2oo-k.w.  2,300- 
volt,  3-phase,  vertical  alternators  of  the  revolving  field  type,  and 
are  operated  at  200  revolutions  per  minute. 

In  some  localities,  where  it  is  not  practicable  to  develop  electrical 
power  directly,  it  is  possible  to  arrange  for  purchase  of  it  from  a 
source  external  to  the  project,  and  to  obtain  this  at  rates  notably  low, 
because  of  the  fact  that  the  power  can  be  utilized  in  pumping  at 
times  of  day  or  during  seasons  when  there  is  least  demand  for  it  for 
use  in  other  purposes,  for  example,  in  any  large  electrical  power 
development  for  ordinary  commercial  purposes,  provision  is  made 
for  a  certain  maximum  demand  which  usually  occurs  during  the 
winter  and  within  certain  portions  of  each  day.  At  times  during 
each  day,  or  after  midnight  and  from  then  nearly  to  sundown  there 
is  an  excess  of  power  which  may  be  had  at  small  cost  or  at  rates 
sufficiently  low  to  justify  pumping  for  irrigation. 

There  are  several  modifying  conditions,  however,  which  must  be 
very  carefully  considered,  the  first  of  these  is  that  of  securing  long 
time  contracts  or  provisions  such  as  will  justify  agriculture  operations. 
It  would  be  unwise  to  build  a  pumping  plant  for  an  orchard  which 
will  not  come  into  bearing  for  several  years,  nor  reach  maturity  for 
ten  or  twelve  years,  unless  there  is  assurance  that  the  power  supply 
will  be  adequate  and  can  be  had  at  reasonable  rates  for  a  long  period 
of  years. 

Where  water-power  can  thus  be  had  in  connection  with  irrigation 
development,  the  engineer  should  give  careful  consideration  to  the 
economies  which  may  result  by  extending  the  irrigable  area  to  lands 
which,  lying  above  the  main  canal,  usually  possess  points  of  supe- 
riority either  in  soil,  exposure  or  drainage.  It  frequently  happens 
that  excess  water  accumulates  on  the  low  lands,  reducing  the  value 
of  these.  It  is  sometimes  possible,  under  such  conditions,  to  utilize 
cheap  power  transmitted  by  electrical  devices  in  draining  these  lands, 
this  waste  water  being  used  for  the  reclamation  of  additional  areas. 
Where  drainage  waters  are  used  for  irrigation,  attention  must  be 
given  to  their  quality,  as  they  frequently  contain  large  quantities  of 
harmful  alkali  salts  in  solution. 

In  considering  hydroelectric  developments  of  this  character, 
the  units  commonly  employed  are  the  cubic  foot  per  second  for  rate 
of  flow  and  the  horse-power  or  kilowatt  (i.  h.p.  =  0.746  kw.  or  i  kw.  = 
1.340  h.p.).  Assuming  the  weight  of  water  as  62.5  Ib.  per  cubic  foot, 
this  amount  falling  i  ft.  per  second  develops  0.1136  h.p.  =  0.0847  kw. 
Putting  it  another  way,  i  cu.  ft.  per  second  falling  8.8  ft.  generates 


130      PRINCIPLES  OF  IRRIGATION  ENGINEERING 


y-y 


IRRIGA TION  BY  P UMPING  131 

one  theoretical  horse-power,  or  i  kw.  per  hour  equals  i  acre-foot 
raised  i  ft.  high.  If  for  convenience  in  preliminary  calculations  a 
motor  efficiency  of  80  per  cent,  is  assumed,  i  second-foot  falling 
ii  ft.  will  generate  i  h.p.  or  0.746  kw.  (or  i  kw.  =  1.340  h.p.). 
If  the  power  is  used  for  pumping  water  and  the  plant  efficiency  is 
taken  at  50  per  cent,  for  motor,  pump,  etc.,  then  i  acre-foot  raised 
i  ft.  high  will  require  at  least  2  kw.-hours.  By  this  simple  rule  the 
total  power  required  to  irrigate  an  acre  may  be  apprehended  by 
easy  mental  effort. 

In  estimating  the  energy  created  by  falling  water,  it  is  convenient 
to  make  certain  assumptions,  as  to  the  efficiency  of  the  various 
forms  of  apparatus.  The  turbine  water-wheel  is  assumed  to  have 
an  efficiency  under  good  conditions  of  80  per  cent,  or  over,  some 
have  reached  in  practice  87  per  cent,  or  even  90  per  cent,  on  tests. 
The  generator  may  reach  an  efficiency  of  90  to  95  per  cent.  From 
this  it  is  customary  to  transform  the  power  to  a  higher  voltage  for 
purposes  of  transmission  and  the  transformer  may  be  considered  as 
having  96  to  98  per  cent,  net  efficiency.  There  are  certain  losses  in 
transmission  line  which  may  vary  from  5  to  10  per  cent.,  and  it  is 
fair  to  assume  a  transmission-line  loss  of  this  amount.  Transforming 
the  power  again  and  reducing  its  voltage  is  another  loss  of  2  or  3 
per  cent,  or  more,  so  that  the  horse-power  ultimately  transmitted 
will  be  about  as  follows: 

ASSUMED  EFFICIENCIES 

Turbines 80  per  cent,  net  efficiency 80. o 

Generator 93  per  cent,  net  efficiency 74.4 

Transformer 97  per  cent,  net  efficiency 72.  2 

Transmission  line 92  per  cent,  net  efficiency 66.4 

Transformer 97  per  cent,  net  efficiency 64.4 

Starting  thus,  with  a  theoretical  1,000  h.p.  we  arrive  at  the  point 
of  use  with  about  644  h.p.  applied  to  the  motors. 

The  cost  of  power  installation  varies  widely  with  the  amount  of 
power  developed,  the  character  of  machinery,  and  the  surrounding 
conditions.  For  preliminary  assumptions  it  may  be  considered  as 
ranging  from  $45  to  $80  per  horse-power,  depending  upon  the 
amount  of  hydraulic  work  necessary  in  the  way  of  dams,  power, 
canals,  etc.  The  cost  of  a  pumping  plant  where  large  pumps  are 
used  may  vary  from  $45  to  $65  per  horse-power,  making  the  cost  of 
a  plant,  ranging  in  capacity  from  1,000  to  5,000  h.p.,  from  $100  to 


132      PRINCIPLES  OF  IRRIGATION  ENGINEERING 

$175  per  horse-power  when  completely  installed,  with  transmission 
lines  and  other  accessories. 

The  cost  of  operation  also  varies  greatly  with  the  character  of  the 
plant  and  the  continuity  of  operation  and  amount  of  power  used. 
It  is  for  this  reason  impossible  to  give  figures  on  the  cost  of  operation 
which  will  be  of  value  in  any  particular  case.  In  pumping  for 
irrigation  the  plant  must  lie  idle  a  considerable  part  of  the  year, 
unless  it  can  be  used  for  other  purposes,  for  example,  as  an  auxiliary 
power  for  domestic  or  municipal  supply.  Under  these  conditions 
it  may  be  possible  to  dispose  of  power  at  very  low  rates  during  the 
winter  season  sufficient  to  justify  the  operation  of  the  plant  in 
order  to  maintain  the  operating  force  and  prevent  increase  of  operat- 
ing cost  due  to  new  organization  each  year. 

In  estimating  the  cost  per  unit  of  horse-power  or  kilowatt-hour, 
it  is  necessary  to  make  certain  assumptions  concerning  the  load 
factor,  that  is  to  say,  the  ratio  between  the  actual  amount  of  power 
which  can  be  developed  continuously  and  the  amount  which  is 
habitually  being  used.  In  other  words,  if  under  normal  conditions 
machinery  is  capable  of  developing  100  h.p.  but  the  average  demand 
throughout  the  day  is  for  only  75  h.p.  the  load  factor  may  be  con- 
sidered as  75.  During  the  day  at  short  intervals  there  may  be  an 
overload  and  the  electrical  machinery  is  usually  built  to  carry  for 
brief  intervals  an  overload  of  50  per  cent,  or  more.  Again  the  load 
may  drop  down  to  a  very  small  fraction  of  the  total  capacity  of  the 
plant,  so  that  the  average  throughout  the  day  under  general  condi- 
tions rarely  approaches  100  per  cent. 

In  estimating  the  economy  of  installation  of  a  power  plant,  it  is 
essential  to  consider  the  probable  cost  of  this  in  comparison  with  the 
possibility  of  purchasing  power,  especially  where  it  may  be  obtained 
at  irregular  intervals,  when  not  needed  for  other  purposes,  and  at 
correspondingly  low  prices. 

Assuming  that  electric  power  can  be  purchased  for  pumping 
at  i  cent  per  kilowatt-hour  at  the  switchboard,  and  that  the  pumps 
will  be  operated  for  six  months  in  the  year  of  180  days  continuously, 
with  a  load  factor  of  75,  the  cost  per  100  kw.  for  the  season  will  be 
$3,240. 

The  equivalent  of  this  is  134  h.p.  and  this  amount  will  raise  23  + 
second-feet  of  water  to  a  height  of  50  ft.  serving  for  the  irrigation, 
assuming  an  average  duty  of  water  of  about  2,300  acres,  at  a  cost 
of  $3,240,  or  less  than  $1.50  per  acre  for  power. 

Cost  of  Pumping. — This  is  expressed  either  in  terms  of  quantity 


IRRIGATION  BY  PUMPING  133 

of  water  delivered  at  a  certain  point,  such  for  example  as  $i  per  acre- 
foot  or  30  cents  per  million  gallons,  or  more  generally  in  the  terms 
of  acreage  served,  as  $2.50  per  acre  per  season — the  latter  involving 
an  assumption  as  to  the  duty  of  water.  In  discussing  the  matter 
from  an  agricultural  standpoint,  it  is  advantageous  to  use  the  cost 
per  acre  for  direct  comparison  with  cost  of  irrigation  by  gravity 
systems,  and  with  the  value  of  crop  obtained. 

As  a  rule,  the  cost  of  pumping  water  is  higher  than  that  of  obtain- 
ing it  from  gravity  sources.  The  first,  or  construction  cost,  may 
possibly  be  less  than  that  of  a  gravity  system,  but  the  annual 
expense  for  operation  and  maintenance,  including  depreciation, 
is  considerably  higher.  The  cost  is  roughly  proportioned  to  the 
height  to  which  the  water  is  raised,  so  that  the  controlling  factor  is 
largely  the  difference  in  elevation  between  the  source  of  water  in 
the  well,  reservoir,  or  steam,  and  the  point  of  delivery  from  which 
it  reaches  the  irrigable  land. 

Where  the  values  of  crops  are  very  great  as  is  the  case  in  some 
of  the  highly  developed  fruit  sections  and  with  sugar-cane  in  the 
Hawaiian  Islands,  water  for  irrigation  may  be  pumped  to  a  height 
of  500  ft.  or  more.  With  ordinary  crops  of  the  temperate  zone  the 
present  economical  lift  is  considered  as  being  not  far  from  60  or  70 
ft.  Theoretically,  it  should  be  profitable  to  pump  to  greater  heights 
than  these,  but  practically,  this  has  not  yet  been  successfully 
done. 

In  some  sections  the  annual  charges  for  pumping  water  is  not 
less  than  $25  per  acre,  as  for  example,  in  the  foot-hill  region  near 
Pomona  and  Ontario  and  in  Orange  County,  California.  In  other 
sections  where  more  favorable  conditions  obtain,  the  charges 
probably  do  not  exceed  $5  per  acre  per  annum.  Under  exceptional 
conditions  they  may  be  even  less  than  this. 

In  Western  Kansas  the  cost  is  stated  to  be  not  far  from  7  cents 
per  acre-foot  of  water  raised  one  foot  in  height,  or  $3.50  per  acre- 
foot  raised  to  a  height  of  50  ft.  These  figures  roughly  indicate  the 
present  condition  of  development  of  the  small  pumping  plants. 
They  include  operation  and  maintenance,  depreciation  and  interest 
on  investment,  costs  of  5  cents  per  acre-foot  raised  one  foot  are  not 
unusual  and  with  better  economy  the  cost  is  stated  to  be  as  low  as  3 
cents  or  slightly  less.  These  lower  estimates  are  generally  based  not 
on  long-continued  actual  practice  but  on  short- time  or  laboratory 
tests.  The  general  appearance  of  the  pumping  plant  and  reservoir 
is  shown  in  Plate  IX,  Fig.  B. 


134      PRINCIPLES  OF  IRRIGATION  ENGINEERING 

It  is  difficult  to  obtain  actual  costs  of  pumping  because  of  the 
fact  that  many  of  the  private  plants  have  been  operated  in  the 
interests  of  the  promoters  or  persons  selling  land  and  at  a  nominal 
charge  for  the  purpose  of  facilitating  land  sales.  It  is  generally 
agreed  that  at  a  later  date  when  the  land  is  sold  the  works  will  be 
turned  over  to  the  land  owners  to  be  operated  at  their  expense. 
The  losses  which  may  be  encountered  in  cost  of  operation  during 
the  time  when  the  plant  is  new  and  the  lands  are  being  placed  on 
the  market  are  more  than  made  up  by  the  additional  prices  received 
from  the  sale  of  lands.  This  fact  is  cited  so  that  engineers  may  not 
be  misled  by  the  relatively  low  annual  charges  occasionally  quoted 
for  pumped  water,  these  not  necessarily  representing  the  actual 
cost,  which  in  some  cases  may  be  twice  as  great. 

Feasibility  of  Pumping. — The  practicability  of  pumping  water 
for  irrigation  is  governed  primarily  by  natural  conditions,  such  as 
place  of  occurrence  of  water,  height  of  lift,  distance  to  the  irrigable 
land,  and  mechanical  difficulties  growing  out  of  these,  all  being 
summed  up  in  the  statement  of  probable  cost.  There  may  be  an 
ample  supply  of  water,  and  relatively  cheap  power,  but  the  lands 
to  be  covered  may  be  widely  scattered  in  small  tracts  requiring 
long  pressure  pipe  or  distributing  system  over  ground  too  rough  or 
undulating  to  render  the  work  successful,  or  the  distance  to  markets 
may  be  too  great.  It  is  necessary,  therefore,  in  considering  this 
matter  of  obtaining  water  to  take  into  account,  as  in  the  case  of 
gravity  systems,  the  economic  as  well  as  the  engineering  features, 
such  as  the  quality  of  the  soil,  the  ease  of  irrigation,  the  climatic 
conditions  and  markets  governing  the  value  of  crops,  and  to  study 
these  in  connection  with  the  more  purely  mechanical  side. 

As  stated  in  the  paragraphs  regarding  cost,  it  has  not  been  found 
feasible  as  a  rule  to  pump  water  for  ordinary  crops  in  the  temperate 
zone  to  a  height  much  greater  than  70  ft.,  but  there  are  conditions 
where  small  tracts  of  land  of  exceptional  quality  and  accessible  to 
markets  will  justify  the  building  of  a  pumping  plant  for  raising 
water  beyond  this  height. 

The  feasibility  of  extending  the  agricultural  area  by  pumping  is 
governed  by  the  comparison  of  total  costs  with  returns.  Of  the 
total  costs,  the  item  of  power  is  frequently  the  large  and  controlling 
one.  It  is  apparent  that  while  at  present  this  cost  must  be  kept  at 
a  relatively  low  amount,  as  time  goes  on,  as  the  soil  is  subdued 
and  rendered  more  productive,  as  the  orchards  reach  maturity,  and 
as  population  increases  and  markets  are  established,  it  will  be 


IRRIGATION  BY  PUMPING  135 

possible  to  incur  a  larger  and  larger  cost  per  acre  and  to  utilize 
sources  of  power  which  at  the  present  time  are  considered  as  being 
too  expensive. 

The  growth  of  the  country  is  accompanied  by  an  improvement 
in  mechanical  appliances  and  in  the  feasibility  of  purchasing  waste 
or  excess  power  from  various  industrial  processes.  As  before 
stated,  the  excess  power  from  lighting  or  transmission  plants  may 
be  purchased  and  used  when  not  in  demand  for  the  primary  purpose 
for  which  the  machinery  was  installed.  These  considerations 
should  be  given  due  weight  in  all  plans  for  developing  irrigation  by 
pumping,  and  before  stating  the  limit  to  any  proposed  system,  these 
ultimate  sources  of  power  should  be  carefully  studied. 

The  maximum  height  of  lift  which  may  be  considered  in  planning 
a  pumping  plant  for  irrigation  has  previously  been  given  as  ranging 
from  a  present  maximum  of  over  500  ft.  for  the  most  valuable 
tropical  plants,  citrus  fruits  and  intensive  truck  farming,  down  to 
60  or  70  ft.  for  the  ordinary  crops  of  the  temperate  zone.  The 
controlling  factor  of  height  of  lift  is  not  set  by  mechanical  con- 
siderations, but  in  each  case  these  enter  into  the  designing  of  the 
plant  after  determination  has  been  made  of  the  limit  of  cost  which 
may  be  incurred. 

In  southern  California,  in  the  vicinity  of  Los  Angeles,  water  is 
being  pumped  as  high  as  75  ft.  for  the  purpose  of  raising  alfalfa,  and 
as  this  is  one  of  the  crops  which  requires  a  large  amount  of  water, 
it  may  be  assumed  that  if  this  can  be  successfully  grown  by  pump- 
ing water  to  this  height,  orchards  and  more  valuable  crops  may  be 
cultivated  with  water  lifted  still  higher.  Each  year  the  area  of 
alfalfa  thus  irrigated  is  being  extended,  indicating  that  the  operations 
are  financially  successful. 


CHAPTER  VIII 
DRAINAGE 

Classification. — The  subject  of  drainage  may,  in  a  general  way, 
be  subdivided  into  two  classes;  namely,  surface  drainage  and  under- 
ground drainage.  These  two  classes  are  not  entirely  independent, 
since  it  would  be  impossible  to  carry  on  any  form  of  surface  drainage 
without  producing  a  certain  amount  of  underground  drainage,  and 
equally  impossible  to  carry  on  underground  drainage  without  also 
at  certain  times  disposing  of  surface  waters. 

Surface  drainage  ordinarily  applies  to  the  removal  from  the  sur- 
face of  the  ground  waters  which  have  fallen  upon  it  in  the  form  of 
rain  or  snow.  Surface  drains  are  usually  comparatively  shallow 
open  drains  of  sufficient  capacity  to  take  care  of  storm  floods  and 
carry  them  away  quickly  and  before  they  have  time  to  soak  to  any 
considerable  depth  into  the  soil. 

Underground  drainage  applies  to  the  removal  of  ground  waters, 
or  those  which  are  below  the  surface  of  the  soil.  These  ground 
waters  may  be  the  result  of  rains  or  irrigation  in  the  immediate 
vicinity,  or  they  may  be  carried  for  some  distance  underground 
and  finally  come  near  the  surface  on  the  lower  areas  in  the  path  of 
their  flow.  Underground  drains  may  be  either  open  or  closed; 
they  differ,  however,  from  surface  drains  in  that  the  supply  reaches 
them  not  over  the  surface  but  through  the  lower  soil  or  sub-soil. 

Drainage  problems  in  connection  with  irrigation  usually  require 
the  use  of  underground  drains  since  it  is  the  excess  of  irrigation 
waters  that  have  been  put  into  the  soils  that  have  to  be  removed. 
As  this  work  is  intended  to  deal  only  with  problems  of  irrigation, 
underground  drainage  will  be  the  principal  subject  treated  in  this 
chapter. 

Needs  of  Drainage. — One  of  the  first  requisites  for  the  growth 
of  crops  is  moisture.  The  soil  must  be  kept  sufficiently  wet  to 
supply  to  the  roots  of  a  plant  the  water  which  it  requires  for  its 
existence  and  growth. 

Soils  are  made  up  of  minute  particles  very  irregular  in  shape  and 
size.  These  particles  when  loosely  thrown  together,  as  is  the  case 
in  properly  cultivated  soils,  leave  spaces  of  irregular  shape  and 

136 


DRAINAGE  137 

dimensions  between  them.  The  size  of  the  spaces  depend  upon 
the  size  and  shape  of  the  particles  forming  the  soil  and  the  closeness 
of  the  particles  to  each  other.  It  thus  follows  that  a  closely  packed 
soil  of  the  same  material  will  absorb  and  hold  less  water  than  one 
which  is  loosely  broken  up,  for  the  reason  that  the  volume  of  the 
spaces  between  the  particles  is  less  in  the  former  than  in  the  latter 
case. 

Each  individual  particle  comprising  a  soil,  due  to  the  law  of 
attration  of  matter,  is  capable  of  holding  on  its  surface  a  minutely 
thin  film  of  water.  The  mutual  attraction  between  the  particle  and 
this  thin  film  is  so  great  that  all  the  water  cannot  be  drained  out  of  a 
soil  by  gravity;  in  fact,  to  remove  all  of  the  moisture  which  clings  to 
the  minute  particles  of  a  soil  except  by  carefully  heating  and  dry- 
ing is  a  very  difficult  process. 

When  a  soil  contains  no  perceptible  water  adhering  to  its  indi- 
vidual particles,  it  is  said  to  be  dry;  when  it  contains  only  so  much 
water  as  is  held  by  the  attraction  of  the  particles  and  no  more 
will  drain  away,  it  is  said  to  be  moist;  when  the  spaces  between  the 
particles  are  completely  filled  with  water,  it  is  said  to  be  saturated. 
If  an  excavation  be  made  in  soil  which  is  moist  only,  no  water  will 
flow  from  the  soil  into  the  excavation.  If  the  excavation  be  made 
in  soil  that  is  saturated,  water  will  collect  and  in  a  short  time  stand, 
at  the  same  elevation  as  the  top  of  the  saturated  soil.  The  surface 
of  free  water  or  the  upper  limit  of  saturation  in  a  soil  is  commonly 
called  the  water  plane. 

Vegetation  requires  moisture,  but  with  the  exception  of  aquatic 
plants,  will  not  grow  in  soils  that  are  saturated  with  water.  In 
order  to  grow  crops  in  an  arid  or  semi-arid  region — where  the 
natural  rainfall  is  not  sufficient  to  supply  the  necessary  moistures 
to  the  soils — this  lack  of  water  must  be  supplied  by  irrigation. 
Important  as  the  supplying  of  water  to  land  may  be,  it  is  equally 
important  that  any  excess  water  which  would  cause  the  soil  to  be- 
come saturated  be  removed.  Theoretically  it  may  seem  possible  to 
apply  to  soils  only  the  exact  amount  of  water  required  for  the  growing 
of  crops.  Practically  it  is  found  that  in  nearly  every  case  there  is  a 
certain  amount  of  excess  water  which  must  be  disposed  of.  When 
the  soil  is  open  or  porous  to  a  sufficient  depth  to  permit  the  excess 
waters  being  carried .  away ,  natural  drainage  may  be  said  to  exist. 
Where  nature  has  not  provided  natural  underground  drainage,  it 
must  be  supplied  artificially. 

The  fundamental  problem  in  drainage  is  to  control  the  elevation 


138      PRINCIPLES  OF  IRRIGATION  ENGINEERING 

of  the  water  plane  and  keep  it  below  the  zone  of  soil  required  for  the 
roots  of  growing  plants.  If  this  is  not  done  the  roots  cannot  pene- 
trate to  the  required  depth  to  obtain  the  necessary  nourishment 
from  the  soil. 

In  soils  which  contain  harmful  alkali  salts,  it  is  necessary  also 
that  the  water  plane  be  kept  down  in  order  to  prevent  on  accumula- 
tion of  these  salts  on  the  surface. 

Alkali  and  its  Effect. — As  heretofore  stated  the  soils  of  the  arid 
and  semi-arid  regions  are  largely  the  results  of  disintegration  of 
rock.  Many  of  them  have  not  been  completely  washed  by  copious 
rains  during  their  formation  and  contain  large  quantities  of  soluble 
mineral  salts.  Some  of  these  salts,  especially  in  limited  quantities, 
are  beneficial  and  necessary  for  the  growth  of  vegetation,  while 
others  are  harmful,  and  in  sufficient  quantities  will  prohibit  its 
growth.  Sodium  carbonate,  commonly  known  as  black  alkali,  is 
the  most  detrimental  of  all  the  alkali  salts  to  plant  growth.  The 
exact  action  of  alkali  on  a  plant  is  not  clearly  understood,  its  effect, 
however,  is  to  destroy  the  root  tissues  near  the  surface  of  the  soil 
and  leave  the  plant  to  die  for  lack  of  food  and  moisture.  On  account 
of  the  action  of  alkali  being  near  the  surface  it  is  essential  that  any 
accumulation  of  salts  in  the  top  stratum  of  soil  be  avoided.  (See 
.Plate  X,  Fig.  A.) 

In  their  natural  state  the  alkali  salts  are  distributed  more  or  less 
uniformly  through  the  soils,  frequently  extending  to  considerable 
depths.  When  water  is  applied  to  the  land,  the  soluble  salts  are 
dissolved.  As  the  process  of  evaporation  goes  on  from  the  surface 
of  the  soil  and  waters  charged  with  alkali  are  brought  up  by  capillary 
action  there  is  a  gradual  accumulation  of  salts  on  or  near  the  surface 
until  finally  the  soil  is  unfit  for  the  growing  of  crops.  If  the  soil 
becomes  saturated  or,  in  other  words,  if  the  water  plane  is  brought 
near  to  the  surface,  the  capillary  action  in  drawing  water  to  the 
surface  and  consequently  the  rate  of  evaporation  and  deposit  of 
alkali  is  increased. 

Benefit  of  Drainage. — Reference  has  already  been  made  to  the 
necessity  of  artificial  drainage  on  certain  classes  of  soils  to  prevent 
their  becoming  unfit  for  use  through  the  rise  of  the  water  plane  and 
the  accumulation  on  the  surface  of  harmful  alkali  salts.  On  certain 
other  classes  of  soils  crops  can  be  grown  without  drainage,  but  the 
soils  are  greatly  improved  and  the  value  of  the  crop  yield  increased 
by  its  use.  In  such  cases  drainage  may  be  classed  as  a  benefit 
rather  than  a  necessity.  In  this  respect  it  may  be  compared  to  any 


PLATE  X 


FIG.  A. — Alkali  flat,  formerly  a  valuable  farm,  now  ruined  by  careless  irrigation 
and  lack  of  drainage. 


FIG.  B. — Distributory  lined  with  concrete  to  reduce  loss  of  water  and  prevent 
development  of  alkali. 

(Facing  Page  138) 


PLATE  X 


FIG.  C. — Weir  and  self-registering  gage.     Williston  Project,  No.  Dak. 


FIG.  D. — Automatic  gage  for  recording  height  of  water  in  river  or  main  canal. 
Laramie  River,  Colo. 


DRAINAGE  139 

other  method  of  improving  the  soil  or  increasing  the  amount  of 
crop  that  can  be  grown.  For  example,  on  many  soils  crops  will 
grow  without  the  use  of  fertilizer,  but  it  has  been  found  that  by 
its  use  the  value  of  the  crop  may  be  increased  by  many  times  the 
cost  of  the  fertilizer  applied  to  the  land. 

Soils  that  are  especially  benefited  by  drainage  are  those  which  on 
account  of  their  compactness  do  not  allow  a  free  movement  of  water 
through  them.  Soils  must  contain,  in  addition  to  moisture,  a 
certain  amount  of  air,  in  order  that  they  be  in  proper  condition  to 
grow  crops.  It  is  necessary  also  that  they  be  sufficiently  loose  and 
porous  to  allow  the  plant  roots  to  penetrate  them  freely.  It  is 
possible  for  a  soil  to  become  so  firmly  compacted  that  there  are 
practically  no  spaces  between  its  particles  and  consequently  it  is 
impossible  for  either  air  or  water  to  enter  freely.  Soil  in  this  condi- 
tion is  commonly  designated  as  water-logged,  although  the  amount 
of  water  it  contains  is  small  on  account  of  the  lack  of  spaces  between 
the  particles  to  take  up  and  hold  moisture.  A  water-logged  soil  is 
cold  due  to  the  lack  of  the  circulation  of  air  through  it.  For  this 
reason  crops  cannot  be  started  as  early  in  the  spring  on  a  water- 
logged soil  as  on  a  loose  and  porous  one. 

By  providing  for  the  removal  of  water  from  the  lower  strata  of 
a  water-logged  soil  by  means  of  drainage  and  at  the  same  time  break- 
ing up  the  surface  by  deep  plowing  or  sub-soiling,  the  .pores  of  the 
soil  may  be  opened  and  a  downward  movement  of  water  started. 
Air  will  be  drawn  into  the  soil,  following  the  movement  of  water 
through  it  and  in  this  manner  the  soil  will  be  warmed  and  brought 
to  the  proper  condition  for  growing  crops. 

Another  important  advantage  of  getting  a  downward  motion  of 
water  started  and  air  drawn  into  the  soil  by  drainage  is  the  removal 
of  impure  or  objectionable  vegetable  matter.  The  roots  of  vege- 
tation, it  appears  from  recent  agricultural  investigations,  leave  in 
the  soil  a  certain  amount  of  organic  matter,  a  portion  of  which  is 
detrimental  to  some  kinds  of  plant  growth.  The  aeration  of  the 
soil  carries  into  it  the  necessary  elements  for  reducing  the  organic 
matter  left  in  the  soil  by  vegetation  to  a  state  that  is  less  harmful 
to  the  growth  of  crops. 

Summarizing,  drainage  may  be  said  to  be  a  protection  against 
injury  to  land  by  raising  the  water  plane  too  near  the  surface,  and 
the  bringing  to  the  top  soil,  through  capillary  action  and  evapora- 
tion, harmful  alkali  salts.  It  is  also  an  insurance  of  larger  and  better 
crop  yields  by  keeping  the  pores  of  the  soil  open,  thus  permitting 


140      PRINCIPLES  OF  IRRIGATION  ENGINEERING 

it  to  be  warmed  and  purified  through  aeration,  and  kept  in  proper 
condition.  It  will  also  be  shown  later  that  drainage  is  beneficial 
in  reducing  the  amount  of  water  which  must  be  applied  to  the  soil 
in  the  process  of  irrigation. 

Ground  Water. — The  term  ground  water  as  here  used  applies 
ordinarily  to  water  below  the  surface  of  the  soil.  The  upper  limit 
of  ground  water  is  the  top  of  the  zone  of  saturation  in  the  soil  or 
what  has  already  been  defined  as  the  water  plane.  In  some  special 
instances  the  water  plane  may  rise  until  it  is  above  the  ground  sur- 
face, as  for  example  in  low  depressions.  The  elevation  of  the  ground 
water  in  such  cases  will  be  regulated  and  controlled  by  sub-surface 
waters  in  the  higher  adjacent  areas.  Water  which  has  been  brought 
to  or  above  the  surface  by  the  rise  of  the  water  plane  and  the  eleva- 
tion of  which  is  controlled  by  an  underground  movement  of  water 
may  properly  be  classed  as  ground  waters. 

The  depths  of  ground  water  varies  greatly  in  different  formations, 
and  in  a  comparatively  small  area,  say  of  i  or  2  square  miles,  may 
range  anywhere  from  i  to  100  ft.  or  more.  It  depends  largely 
upon  the  depth  to  impervious  material,1  such  for  example,  as  a 
strata  of  clay  or  rock.  It  also  depends  upon  the  rate  at  which 
water  will  move  through  the  pervious  top  strata,  and  the  quantity 
of  water  which  reaches  the  area,  either  in  the  form  of  rain  or  as 
applied  for  irrigation. 

If  a  sub-soil  is  porous,  the  excess  water  which  finds  its  way  into 
it  will  gradually  pass  downward  until  it  reaches  an  impervious 
stratum  which  prevents  further  downward  motion.  When  the 
surface  of  the  impervious  stratum  is  level  or  inclined  downward, 
the  water  will  move  laterally  over  it  until  it  finally  finds  its  way  to 
some  natural  outlet  and  is  carried  away.  In  this  manner  the  water 
plane,  if  the  supply  which  reaches  the  surface  is  not  too  great,  may 
be  kept  down  through  natural  process.  If  the  surface  of  the  imper- 
vious stratum  is  irregular  consisting,  as  is  frequently  the  case,  of 
depressions  and  ridges,  the  lateral  movement  is  prevented  and  the 
water  plane  will  rise  until  an  outlet  is  found  over  the  crest  or  through 
gaps  in  the  impervious  barriers.  It  thus  follows  that  even  with  a 

1  Note. — Materials  which  are  absolutely  impervious  to  water  are  seldom  found 
in  nature.  For  want  of  a  better  term  impervious  material  is  used  in  this  chapter 
to  designate  material  which  is  tight  enough  to  prevent  the  passage  of  but  a  very 
limited  quantity  of  water  through  it,  such  for  example  as  firm  clay  or  rock  in 
place. 

There  is  no  sharp  line  of  demarcation  between  pervious  and  impervious  mate- 
rials as  found  in  nature;  both  are  therefore  to  be  considered  as  relative  terms  only. 


DRAINAGE  141 

seemingly  porous  sub-soil  of  considerable  depth  the  water  plane 
may  be  held  up  near  the  surface  by  the  existence  of  impervious  under- 
ground ridges  or  dikes. 

When  the  amount  of  water  which  reaches  a  sub-soil  is  greater 
than  can  be  carried  away  laterally  over  the  impervious  stratum, 
even  though  its  surface  be  level,  the  sub-soil  will  become  saturated 
and  the  water  plane  rise  until  it  reaches  the  surface  or  until  equi- 
librium of  inflow  and  outflow  is  established.  In  the  arid  or  semi- 
arid  regions  where  irrigation  has  not  been  practised,  ground  waters 
are  usually  found  at  a  considerable  distance  below  the  surface; 
this  is  on  account  of  the  limited  rainfall  and  correspondingly  small 
amount  of  water  which  reaches  the  sub-soils. 

The  rate  of  lateral  movement  of  ground  waters  depends  upon  the 
porosity  of  the  material  and  also  the  grade  or  slope  of  the  water 
plane.  A  compact  formation  resists  the  flow  of  water  first  on  ac- 
count of  the  total  cross-sectional  areas  of  the  openings  through  it 
being  small,  and  second,  on  account  of  the  minute  size  of  each  of 
these  openings,  since  greater  pressure  is  required  to  force  water 
through  them.  On  account  of  the  complex  nature  of  this  subject, 
it  is  impossible  to  apply  any  theory  to  determine  the  porosity  of 
a  soil,  in  so  far  as  it. will  affect  the  passage  of  water.  Even  in  the 
most  porous  soils  such  as  sand  or  gravel,  the  rate  of  water  move- 
ment is  very  slow  amounting  to  only  a  few  feet  per  day,  while  in  the 
most  compact  clays  it  is  scarcely  perceptible. 

The  elevation  of  the  water  plane  relative  to  the  surface  of  the  soil 
is  frequently  affected  by  the  varying  thickness  of  a  more  or  less 
porous  stratum  through  which  ground  waters  are  moving.  This 
condition  is  illustrated  by  considering  a  shallow  sub-stratum  of 
sand  or  gravel  underlain  by  a  stratum  of  imprevious  material  and  also 
capped  by  a  soil  of  clay  or  other  semi-impervious  soil.  The  ground 
waters  will  move  through  the  stratum  of  sand  or  gravel  as  this  offers 
the  least  resistance  to  flow.  If  the  thickness  of  this  porous  stratum 
is  uniform  or  nearly  so  the  movement  of  the  waters  will  be  uniform 
and  but  little  if  any  upward  pressure  will  be  exerted  against  the  less 
pervious  top  stratum. 

At  those  places  where  the  thickness  of  the  sand  or  gravel  stratum 
is  diminished,  due  to  thinning  of  the  beds  or  the  presence  of  imper- 
vious dikes  or  barriers  projecting  upward  into  it,  the  flow  will  be 
checked  and  the  ground  water  will  be  put  under  slight  pressure 
which  will  tend  to  force  it  to  the  surface.  Examples  are  frequent  in 
the  irrigated  portions  of  the  arid  west  where  waters  have  traveled 


142      PRINCIPLES  OF  IRRIGATION  ENGINEERING 

underground  for  long  distances  and  are  finally  forced  to  the  surface 
on  account  of  the  porous  sub-soil  being  obstructed  or  pinched  out. 
Conditions  of  this  kind  are  more  likely  to  occur  on  or  near  the  foot  of 
slopes  but  are  also  frequently  found  on  nearly  level  or  uniformly 
sloping  land. 

Information  relative  to  ground  waters  on  a  particular  area  can  be 
obtained  by  means  of  borings  put  down  to  sufficient  depths  to  show 
the  elevation  of  the  water  plane  and  the  character  of  the  soil  and 
sub-soil  materials  over  that  area.  It  is  ordinarily  possible  from  a 
study  of  these  data  to  find  the  direction  of  movement  of  ground 
water  and  to  determine  the  cause  of  the  rise  of  the  water  plane  too 
near  the  surface.  In  many  cases  the  source  of  the  ground  water  can 
also  be  ascertained;  this,  however,  is  not  always  possible  on  account 
of  the  long  distance  it  sometimes  travels  before  coming  to  the 
surface.  It  is  impossible  on  account  of  the  many  unknown  factors 
involved  to  form  accurate  conclusions  relative  to  the  move- 
ment of  ground  waters  from  surface  indications  or  from  theoretical 
considerations. 

Effects  of  Drainage  on  Soils. — Reference  has  already  been  made  to 
the  benefits  to  be  derived  from  drainage.  The  effects  of  drainage 
on  soils  which  serve  as  a  benefit  may  be  enumerated  as  follows: 

1.  Removal  of  excess  water. 

2.  Breaking  up  less  pervious  materials  and  increasing  porosity. 

3.  Washing  out  impurities. 

4.  Increasing  the  capacity  for  retaining  water. 

The  most  important  of  these  is  the  removal  of  excess  waters  from 
the  soil.  Most  useful  plants  cannot  survive  in  a  soil  saturated  with 
water.  The  first  consideration  in  drainage  is  to  draw  down  the 
water  plane  below  the  depth  to  which  the  roots  must  penetrate.  By 
keeping  the  water  plane  well  down  the  roots  are  encouraged  to  go 
deeper  for  water.  The  result  is  a  more  hardy  plant  than  could  be 
grown  if  it  were  required  to  obtain  its  entire  nourishment  from  a  thin 
layer  of  soil  near  the  surface. 

The  breaking  up  and  rendering  the  soil  more  porous  is  accomplished 
by  the  downward  motion  of  the  water  through  it.  This  breaking  up 
of  the  soil  is  also  accomplished  to  a  certain  degree  by  the  roots  of 
plants  penetrating  it.  Nitrogen  is  also  carried  into  the  soil  by  the 
roots  of  certain  plants  and  the  soil  is  thereby  enriched.  The  down- 
ward motion  of  the  water  and  plant  growth  work  together  in  a  well- 
drained  soil  to  disintegrate  it,  rendering  a  thicker  stratum  available 
for  plant  food. 


DRAINAGE  143 

Impurities  existing  in  the  soil  since  its  formation,  as  well  as  those 
which  accumulate,  are  washed  out  by  the  downward  motion  of  water. 
The  soil  is  thereby  kept  in  healthful  condition  so  that  plants  can 
thrive  in  it. 

One  of  the  greatest  benefits  of  the  breaking  up  of  a  soil  and  render- 
ing it  more  porous  is  its  increased  capacity  for  retaining  moisture. 
In  a  loose  soil  the  particles  are  sufficiently  separated  from  each  other 
so  that  when  water  is  applied  each  particle  holds  a  minute  film  of 
moisture  clinging  to  its  surface.  The  water  thus  held  cannot  be 
drained  away  and  evaporation  takes  place  slowly.  The  result  is 
that  moisture  will  be  retained  available  for  the  use  of  plants  much 
longer  in  a  porous  than  in  a  non-porous  soil.  On  account  of  the 
greater  amount  of  moisture  held  by  the  particles  there  is  less  waste 
of  water  also.  Moisture  is  consequently  held  in  suspension  which 
otherwise  in  a  compact  soil  would  be  wasted  over  the  surface  or 
would  have  passed  off  laterally  through  the  surface  layers.  It 
follows  from  this  that  the  total  amount  of  water  which  must  be 
applied  for  the  growing  of  a  crop  may  if  properly  applied  be  less 
in  a  porous  than  a  non-porous  soil.  Well  drained  land,  strange 
as  it  may  appear,  requires  less  water  to  irrigate  it  than  that  which 
is  undrained. 

Open  and  Closed  Drains. — The  relative  merits  of  open  and 
closed  drains  are  questions  largely  of  economy  in  construction  and 
operation.  The  action  of  a  drain  of  given  depth  and  capacity  in 
drawing  waters  laterally  to  it  and  lowering  the  water  plane  is,  so 
far  as  known,  the  same  whether  it  be  open  or  closed.  This  is  assum- 
ing that  each  is  kept  in  proper  condition  to  take  up  the  excess 
waters  from  the  soil  and  carry  them  away.  It  is  claimed  by  some 
that  open  drains  under  certain  conditions  become  silted  along  the 
bottom  and  for  some  distance  up  the  side  slopes  so  that  water  can- 
not enter  them  freely.  Examples  have  been  found  where  the  ground 
water  immediately  adjacent  an  open  drain  stood  above  the  water 
surface  in  the  drain;  this,  however,  was  due  to  an  upward  pressure 
against  a  relatively  impervious  top  soil.  The  drains  where  this 
condition  existed  were  not  cut  deep  enough  to  intercept  the  pervious 
stratum  below. 

In  considering  the  relative  cost  of  construction  of  open  and 
closed  drains  there  must  be  taken  into  account  in  the  former  the 
value  of  the  lands  which  they  occupy  in  addition  to  the  cost  of 
building  the  drains.  Open  drains  are  a  detriment  to  agricultural 
operations  on  account  of  cutting  up  the  lands,  and  the  opportunity 


144      PRINCIPLES  OF  IRRIGATION  ENGINEERING 

which  they  offer  for  the  growth  of  noxious  weeds  and  grasses.  The 
maintenance  of  open  drains  intending  to  regulate  and  control  the 
elevation  of  ground  waters  is  difficult  on  account  of  the  tendency 
to  become  partly  filled  with  weeds  or  other  obstructions.  When 
this  occurs  the  effective  depth  of  the  drain  is  decreased,  and  its 
efficiency  for  drawing  down  the  water  plane  is  lessened.  Open 
drains  have  an  advantage  over  closed  drains  in  that  their  capacity 
is  not  limited  to  a  pipe  or  conduit  of  fixed  dimensions,  but  increases 
as  the  water  plane  in  the  soil  adjacent  to  the  canal  rises. 

On  steep  slopes  it  may  be  necessary  to  construct  drops  in 
open  drains  in  order  to  prevent  erosion;  in  closed  drains  this  is 
ordinarily  unnecessary,  the  increased  grade  being  an  advantage 
in  increasing  the  velocity  of  flow  and  reducing  the  size  of  drain 
required. 

Closed  drains  permit  all  the  land  over  which  they  are  constructed 
being  used,  and  obviate  the  objectional  cutting  of  the  land  by  open 
channels.  When  properly  constructed  they  require  little  or  no 
maintenance  and  are  always  in  a  condition  to  perform  the  function 
for  which  they  are  intended.  In  determining  the  question  whether 
an  open  or  closed  drain  is  to  be  used  in  any  particular  case,  the 
advantages  of  each  from  the  relative  cost  of  construction  and  main- 
tenance and  the  probable  efficiency  for  the  purpose  intended  should 
be  considered. 

In  general,  it  may  be  said  that  the  closed  forms  are  cheaper  and 
better  adapted  for  small  drains  intended  to  remove  excess  waters 
from  the  soil  and  hold  down  the  water  plane.  Open  trenches  are 
ordinarily  cheaper  for  the  larger  trunk  drains  where  a  considerable 
capacity  is  required. 

The  materials  from  which  closed  drains  should  be  constructed 
will  depend  to  a  certain  extent  upon  what  is  available  in  the  particu- 
lar locality  where  used.  Clay  and  cement  tiling,  sewer  pipe  and 
wooden  boxes  have  all  been  successfully  used.  The  choice  of  one 
of  these  is  largely  a  question  of  first  cost  and  permanency  of  con- 
struction. Hard-burned  clay  tiles  of  good  quality,  so  far  as  known, 
are  not  affected  by  any  of  the  various  constituents  found  in  the 
soils  and  when  placed  deep  enough  to  protect  them  from  frost  and 
surface  cultivation  may  be  considered  as  being  as  permanent  as 
ordinary  masonry  construction.  Cement  tiling  may  also  be  con- 
sidered permanent  in  soils  which  do  not  contain  alkali.  In  some 
of  the  soils  of  the  west,  however,  cement  has  been  found  to  be  dis- 
integrated by  the  action  of  alkali  upon  it.  Cement  tiling  for  this 


DRAINAGE  145 

reason  cannot  be  recommended  for  use  in  lands  containing  alkali 
to  any  appreciable  degree. 

Vitrified  sewer  pipe  with  bell  joints  does  not  possess  any  advan- 
tages over  hard-burned  clay  tiling  with  straight  joints.  It  costs 
more  than  the  ordinary  tiling,  and  is  more  difficult  to  put  in  place 
on  account  of  cutting  out  for  the  flanges  in  the  bottom  of  the  trench. 
The  flange  joints  are  also  more  likely  to  become  silted  than  ordinary 
straight  joints.  One  example  has  been  reported  of  a  drainage  line 
made  from  ordinary  vitrified  pipe  where  the  joints  became  sealed 
by  silting  so  that  no  water  could  enter  it.  Wood  on  account  of  its 
tendency  to  decay  cannot  be  considered  as  suitable  material  for 
closed  drains  where  permanency  is  required.  The  decay  of  wood 
in  a  drainage  line  is  hastened  by  the  fact  that  portions  of  the  drain 
may  be  dry  during  a  part  of  each  year. 

On  account  of  the  nature  of  the  work  being  such  that  close  in- 
spection cannot  be  made  of  it  from  time  to  time  and  the  difficulty 
in  finding  and  repairing  breaks  in  a  closed  drain,  permanent  con- 
struction should  be  used  wherever  possible. 

Relief  and  Intercepting  Drains. — Drains  are  sometimes  classed 
as  relief  and  intercepting  depending  upon  the  manner  in  which 
water  reaches  them.  A  relief  drain  is  one  which  taps  a  wet  area 
directly  and  permits  the  ground  water  to  flow  out  from  different 
directions  into  the  drain.  An  intercepting  drain  is  one  intended 
to  cut  off  an  underground  flow  and  carry  away  the  water  before  it 
reaches  an  area  where  the  formation  is  such  that  it  will  rise  to  the 
surface.  Relief  drains  are  adapted  to  lowering  and  keeping  the 
ground  water  at  a  safe  distance  below  the  surface.  They  are  for 
the  most  part  constructed  in  the  lower  portion  of  an  area  to  be 
drained  in  order  to  draw  down  the  ground  water  to  the  lowest 
elevation  possible.  Intercepting  drains,  on  the  other  hand,  are 
constructed  above  the  area  which  they  are  intended  to  benefit. 

Relief  drains  are  of  value  in  loosening  and  increasing  the  porosity 
of  the  soil  by  producing  a  downward  motion  of  water  through  it. 
Intercepting  drains  are,  in  general,  of  no  value  for  this  purpose  since 
they  do  not  as  a  rule  perform  the  function  of  drawing  down  ground 
waters  over  any  considerable  area. 

It  is  impossible  to  compare  the  relative  merits  of  these  two  classes 
of  drains,  on  account  of  the  different  functions  which  they  perform. 
Where  the  drainage  problem  is  to  draw  off  excess  waters  from  a 
large  area  and  improve  the  character  of  the  soil  by  lowering  the 
water  plane  and  inducing  a  downward  motion  of  water  through  it, 
10 


146      PRINCIPLES  OF  IRRIGATION  ENGINEERING 

intercepting  drains  are  not  to  be  considered.  Where  it  is  necessary 
to  remove  ground  waters  which  are  known  to  be  traveling  at  a 
comparatively  shallow  depth  it  can  frequently  be  done  by  means  of 
an  intercepting  drain  constructed  crosswise  to  the  direction  of  the 
flow.  In  order  that  an  intercepting  drain  may  work  effectively  it  is 
essential  that  its  bottom  be  below  the  pervious  stratum  through 
which  the  ground  water  moves.  Where  this  is  not  the  case,  the 
flow  will  continue  through  the  pervious  material  both  from  the  lower 
side  of  the  drain  and  also  under  it.  On  account  of  this  limitation, 
conditions  are  seldom  found  where  it  is  feasible  to  entirely  cut  off 
a  flow  of  ground  water.  Intercepting  drains  may  frequently  be 
used  to  advantage  in  cutting  off  the  greater  portion  of  the  ground 
waters  flowing  down  a  slope,  the  amount  of  drainage  required  on  the 
more  level  lands  below  being  thus  greatly  reduced. 

Drainage  Investigations. — Before  attempting  to  make  plans  for 
the  drainage  of  a  particular  area  as  full  information  as  possible 
relative  to  the  character  of  the  soil  and  position  of  the  water  plane 
should  be  obtained.  In  gathering  facts  relative  to  soil  conditions 
it  is  essential  to  ascertain  whether  the  soil  is  uniform  in  character  to 
the  depth  that  drainage  works  should  be  constructed,  or  whether 
it  is  distinctly  stratified  with  layers  of  clay,  sand  or  gravel;  and  if 
so,  the  porosity  of  the  different  strata.  The  necessity  for  this  in- 
formation lies  in  the  fact  that  the  movement  of  ground  waters 
takes  place  more  freely  in  some  of  these  layers  than  in  others.  In 
planning  drainage  works  it  is  necessary  to  take  account  of  the 
different  carrying  capacities  for  water  of  the  various  strata  of  which 
the  soil  is  composed.  Where  a  somewhat  heavy  and  impervious 
soil,  such,  for  example,  as  clay  or  adobe  is  underlain  by  a  strata  of 
gravel  through  which  water  moves  freely,  it  is  of  the  utmost  impor- 
tance that  the  location  of  the  gravel  be  known  and  that  it  be  taken 
into  consideration  in  planning  works  to  remove  the  excess  water. 

In  addition  to  information  relative  to  the  character  of  soil,  it  is 
necessary  to  carefully  determine  the  elevation  of  water  plane  over 
the  area  to  be  drained.  After  determining  these  facts  it  is  possible 
to  show  graphically,  either  by  contours  of  water  surface  or  by  cross- 
sections,  the  elevation  and  slope  of  the  ground  waters,  and  from  this 
arrive  at  the  direction  of  movement  and  the  most  feasible  location 
for  drains.  It  is  important  also  that,  if  possible,  the  source  of  ground 
waters  be  determined.  This  can  ordinarily  be  done  by  a  study  of 
the  elevation  of  water  surface  and  the  character  of  the  soil  through 
which  the  ground  waters  move. 


DRAINAGE  147 

The  information  required  for  designing  a  drainage  system  usually 
can  be  best  obtained  by  means  of  borings  at  short  distances  apart 
over  the  proposed  area.  The  frequency  of  these  borings  and  the 
depth  to  which  they  should  be  carried  will  vary  in  different  localities, 
due  to  local  conditions.  They  should  be  carried  down  to  a  sufficient 
depth  to  show  the  elevation  of  the  water  plane  and  the  character  of 
soils  for  some  distance  below  the  depth  it  is  necessary  to  drain. 
They  should  be  made  sufficiently  near  each  other  to  enable  the  eleva- 
tion of  the  ground  waters  and  the  character  of  the  underground 
formation  to  be  known  at  any  particular  point  with  a  reasonable 
degree  of  accuracy. 

The  portraying  of  the  water  plane  for  drainage  purposes  is  not 
unlike  the  mapping  by  means  of  contours,  of  the  surface  of  the 
ground  for  other  purposes;  such,  for  example,  as  the  planning  of 
irrigation  canals  and  laterals.  It  must  be  understood,  however, 
that  the  work  of  determining  the  contours  of  a  water  plane  is  far 
less  accurate  than  the  ascertaining  of  surface  contours.  The  same 
is  also  true  of  the  determination  of  the  elevation  and  thickness  of  a 
sub-soil  of  sand  or  gravel.  It  is  essential,  however,  in  planning 
drainage  works  that  as  accurate  data  as  possible  be  had.  The 
source  of  underground  waters  which  rise  sufficiently  near  the  surface 
to  interfere  with  agricultural  operations  is,  in  many  cases,  difficult 
to  determine.  By  drawing  a  series  of  water  contours  or  cross  sec- 
tional profiles  indicating  thereon  the  elevation  of  water  plane  over 
a  given  area,  it  is  ordinarily  possible,  however,  to  trace  out  the 
high-water  areas  and  from  these  a  general  knowledge  is  had  of  the 
local  conditions  and  the  direction  of  percolation  of  the  ground 
water. 

Capacity  of  Drains. — In  arriving  at  the  capacity  of  a  given  drain, 
consideration  must  be  given,  first,  to  the  area  to  be  drained,  and, 
second,  to  the  amount  of  excess  waters  to  be  removed.  In 
estimating  the  area  to  be  drained  by  any  given  drains  or  system 
of  drains,  it  is  necessary  to  take  into  account  not  only  the  area  upon 
which  the  drains  are  constructed  but  the  total  area  of  land  whose 
underground  waters  are  tributary  to  these  drains.  As  before  stated, 
ground  waters  frequently  travel  for  long  distances  at  a  considerable 
depth  and  finally  come  to  the  surface  on  a  comparatively  small  area 
below.  In  determining  the  capacity  of  drainage  works  for  this 
small  area,  particular  attention  must  be  given  to  the  quantity  of 
water  which  reaches  it  from  an  external  source.  At  best,  informa- 
tion of  this  kind  which  can  be  collected  is  only  a  rough  estimate, 


148      PRINCIPLES  OF  IRRIGATION  ENGINEERING 

since  the  amount  of  water  which  flows  away  from  an  irrigated  area 
in  any  particular  direction  cannot  be  accurately  measured. 

The  amount  of  excess  waters  resulting  from  a  given  depth  on  the 
soil,  either  from  natural  rainfall,  or  irrigation,  or  both,  is  also  a 
question  fraught  with  many  uncertainties.  Various  assumptions 
have  been  made  as  to  the  amount  of  water  returned  from  irrigation. 
It  is  doubtful,  however,  if  sufficient  accurately  planned  observations 
have  been  made  on  this  subject  to  warrant  definite  conclusions  being 
based  upon  them.  In  general,  it  is  believed  that  by  careful  super- 
vision of  the  operation  of  applying  water  to  lands,  the  underground 
waste  should  not  exceed  25  per  cent,  of  the  total  amount  applied  to 
the  surface.  If  this  assumption  be  correct,  and  the  amount  of  water 
applied  to  a  particular  tract  during  a  year  is  2  acre-feet,  it  is  sufficient 
to  plan  a  drainage  system  to  remove  1/2  acre-foot  per  acre,  or,  in 
other  words,  a  depth  of  6  in.  over  the  entire  surface. 

Irrigation  ordinarily  takes  place  during  the  summer  months  only, 
say  from  about  the  ist  of  May  until  the  ist  of  October,  a  period  of 
five  months.  It  is  not  necessary  to  make  drainage  works  of  sufficient 
capacity  to  remove  all  of  the  excess  waters  during  the  irrigation 
period,  since  the  soil  has  a  large  storage  capacity  and  drains  will  be 
in  operation  for  all,  or  a  greater  part,  of  the  year.  It  is  believed 
where  the  period  of  irrigation  extends  over  less  than  six  months  of 
the  year  that  twice  the  length  of  irrigation  season  may  be  allowed 
for  the  period  of  operation  of  drains.  That  is  to  say,  where  irriga- 
tion is  carried  on  for  a  period  of  five  months,  a  period  of  ten  months 
may  be  given  for  the  drains  to  remove  the  excess  waters.  If  it  is 
required  to  remove  the  equivalent  of  a  surface  depth  of  6  in.  within 
this  period,  capacity  must  be  provided  in  drainage  ditches  of  i  cu.  ft. 
per  second  for  each  1,200  acres.  The  above  estimates  of  the 
amount  of  water  to  be  removed  as  previously  stated,  are  not  based 
upon  actual  measurements  but  are  believed  to  be  conservative.  It 
is  to  be  understood  that  for  similar  soil  conditions  the  greater  the 
quantity  of  water  used  in  irrigation  the  greater  the  capacity  of 
drains  required. 

Depth  of  Drains. — The  depth  to  which  drains  should  be  con- 
structed depends,  first,  upon  the  character  of  the  soil  as  regards 
water  movement  through  it;  second,  upon  the  capillary  action  of  the 
soil  in  drawing  water  to  the  surface;  and,  third,  upon  the  depth 
below  the  surface  that  the  water  plane  must  be  maintained.  Where 
the  soil  is  underlain  by  a  stratum  of  pervious  sand  or  gravel  con- 
taining water  under  slight  pressure,  it  is  ordinarily  necessary  to 


DRAINAGE  149 

construct  drains  deep  enough  to  tap  this  sand  or  gravel  stratum  and 
relieve  the  pressure  in  order  to  prevent  water  being  forced  to  the 
surface.  Drainage  under  these  conditions  is  not  a  question  of 
putting  down  drains  to  a  depth  of  water  plane  required,  but  rather 
a  question  of  removing  waters  from  below  so  as  to  prevent  their 
being  forced  upward  through  the  soil. stratum  to  the  surface.  Con- 
ditions have  been  found  where  water  has  been  forced  up  to  a  con- 
siderable height  above  the  grade  of  surface  drains  excavated  in  a 
somewhat  pervious  soil. 

In  such  cases  the  lateral  movement  of  water  to  the  drains  is 
not  sufficient  to  carry  water  to  the  drains  as  rapidly  as  it  is  forced 
upward  into  the  soil.  Where  a  pervious  sub-soil  condition  does  not 
exist  and  ground  waters  do  not  reach  the  area  from  an  outside 
source,  attention  must  be  given  to  drawing  off  the  excess  waters 
applied  to  the  surface  only.  When  this  is  the  case,  it  is  necessary 
to  decide  to  what  maximum  elevation  the  water  plane  must  be 
kept.  This  must,  in  every  case,  be  below  the  zone  of  plant  growth. 
It  is  necessary  also  that  it  be  low  enough  so  that  the  capillary  action 
will  not  carry  water  to  the  surface  in  sufficient  quantities  to  cause 
it  to  become  seeped  or  bogged. 

The  distance  that  water  will  rise  by  capillary  action  varies  in 
different  kinds  of  soil.  It  ordinarily  ranges  from  about  i  1/2  to 

3  1/2  ft.     In  general,  it  is  believed  on  irrigated  land,  the  minimum 
depth  to  water  plane  should  not  be  less  than  4  ft.,  while,  for  certain 
kinds  of  crops,  a  greater  depth  may  be  advisable.     The  holding  of 
the  water  plane  down  in  this  manner  allows  the  plant  roots  to 
penetrate  deeper  into  the  soil  and  produces  a  more  vigorous  plant 
than  can  be  obtained  when  growth  is  confined  to  a  shallow  depth. 
The  depth  of  drains  required  to  maintain  a  depth  of  water  plane  of 

4  ft.  will  depend  upon  the  amount  of  water  applied  to  the  soil,  the 
freedom  of  movement  of  water  through  the  ground,  and  the  distance 
between  drains. 

The  above  are  all  questions  which  must  be  determined  for  each 
particular  case  and  it  is  consequently  impossible  to  lay  down  any 
hard  and  fast  rules  relative  to  the  depth  of  drains.  In  general,  it  is 
believed,  however,  that  on  irrigated  lands,  drains  to  be  effective 
should  have  a  minimum  depth  of  not  less  than  about  5  ft.,  while  in 
a  majority  of  cases  a  greater  depth  is  required. 

Distance  between  Drains. — The  proper  distance  between  drains 
in  order  that  they  may  be  effective  and  at  the  same  time  permit  of 
the  most  economic  construction  is,  in  most  cases,  difficult  to  de- 


150      PRINCIPLES  OF  IRRIGATION  ENGINEERING 

termine.  It  depends  primarily  upon  the  rate  of  water  movement 
through  the  soil  and  also  to  some  extent  upon  the  depth  of  the 
drains  and  source  of  ground  waters.  Heavy  surface  soils  underlain 
at  a  comparatively  shallow  depth  by  an  impervious  material  re- 
quire the  most  frequent  drains.  This  is  especially  true  if  the  waters 
to  be  removed  come  from  excess  irrigation  or  rainfall  directly  on 
the  area.  With  conditions  of  this  kind  drains  are  sometimes  re- 
quired at  intervals  of  from  50  to  100  ft.  in  order  to  keep  the  water 
plane  down  to  the  required  depth. 

Where  there  is  a  sub-stratum  of  pervious  material  at  a  reason- 
able distance  below  the  surface  so  the  drains  can  be  cut  into  it  they 
may  be  effective  at  long  distances.  Under  conditions  of  this  kind 
the  effect  of  drains  may  extend  from  half  a  mile  to  a  mile  on  either 
side  of  them.  The  actual  distance  that  the  water  plane  will  be 
lowered  will,  of  course,  depend  upon  the  depth  of  the  drain. 

A  rough  idea  of  the  distance  a  drain  will  draw  water  can  be  had 
from  an  examination  of  the  soil.  Accurate  information,  however, 
can  only  be  obtained  by  observation  on  the  water  movement  and 
slope  of  the  water  plane.  This  can  frequently  be  determined  by  a 
row  of  test  wells  at  right  angles  to  a  natural  drainage  channel. 
Where  topographic  and  other  conditions  will  permit,  it  is  some- 
times advisable  to  construct  short  drains  for  the  purpose  of  study- 
ing their  effect  before  making  final  plans  for  complete  drainage. 
Observations  on  the  effect  of  main  or  trunk  drains  may  also  be  used 
to  determine  the  frequency  of  smaller  drains  that  will  be  required. 

Grades  and  Velocities  of  Flow  in  Drains. — The  most  important 
considerations  in  determining  the  grades  of  drains  is  to  provide  on 
the  one  hand,  sufficient  velocity  to  prevent  the  drains  becoming 
clogged  and,  on  the  other,  to  avoid  excessive  velocities  such  as  tend 
to  erode  the  channels.  The  first  consideration  applies  to  both 
open  and  closed  drains,  while  the  latter  applies  more  especially  to 
open  channels  in  earth  since  closed  drains  are  ordinarily  of  materials 
that  will  withstand  relatively  high  grades  and  velocities.  When 
the  grades  of  earthen  ditches  are  too  high  there  results  a  cutting 
of  the  bottom  or  sides  of  the  channel  which  undermines  the  banks 
causing  them  to  fall.  There  thus  results  an  irregular  and  unsightly 
ditch  where  the  growth  of  noxious  weeds  and  plants  is  encouraged. 
There  may  also  be  a  considerable  waste  of  land  along  the  sides  of 
the  ditch.  If  there  are  any  sections  of  the  ditch  where  the  grades 
are  relatively  flat  the  materials  eroded  above  will  be  deposited  in 
these  sections  and  make  the  problem  of  maintenance  more  difficult. 


DRAINAGE  151 

The  limiting  grades  which  may  be  allowed  in  drainage  ditches 
like  irrigation  canals  will  vary  with  the  amount  of  water  carried 
and  the  character  of  the  materials  through  which  the  drains  are 
constructed.  Special  attention  must  be  given  to  each  particular 
case  in  order  to  determine  the  proper  grade  to  be  used. 

Where  it  is  necessary  to  reduce  the  grade  in  an  open  ditch  to 
prevent  scouring,  some  form  of  drop  should  be  used.  This  may  be 
either  a  vertical  fall  with  a  water  cushion  below  or  a  short  length 
of  channel  built  on  a  steep  grade  and  protected  by  means  of  suitable 
material  to  prevent  erosion. 

The  question  of  grades  and  velocities  in  open  drainage  ditches 
does  not  differ  greatly  from  these  same  questions  when  applied  to 
irrigation  canals.  It  must  be  borne  in  mind,  however,  that  the 
capacity  of  a  drainage  ditch  is  ordinarily  much  less  than  that  of  an 
irrigation  canal  and  that  in  the  former  depth  rather  than  carrying 
capacity  is  the  principal  factor  to  be  considered.  On  account  of 
the  small  capacity  of  drainage  ditches  the  amount  of  grade  which 
they  will  withstand  is  ordinarily  much  greater  than  in  irrigation 
canals.  Drainage  ditches  are  ordinarily  excavated  into  firm 
materials  which  erode  less  freely  than  the  artificial  banks  of  irri- 
gation canals.  For  this  reason  also  the  dangers  of  cutting  in  the 
former  are  less  than  in  the  latter. 


CHAPTER  IX 
OPERATION  AND  MAINTENANCE 

Distribution  of  Water. — The  primary  purpose  of  constructing, 
maintaining  and  operating  a  canal  system  is  to  provide  water  for 
irrigation.  The  ultimate  test  of  the  success  of  the  system  from 
an  engineering,  and  ordinarily  from  a  financial  standpoint,  depends 
upon  whether  the  water  can  be  supplied  to  the  lands  under  it  at 
the  proper  time  when  needed.  This  depends,  first,  upon  the 
character  of  the  design  and  construction,  and  second,  upon  the 
efficiency  of  operation  and  maintenance.  Whatever  the  importance 
of  properly  designing  and  constructing  irrigation  works,  the  im- 
portance of  properly  maintaining  and  operating  them  is  equally  as 
great. 

Operation  and  maintenance  requires  the  determination  of  the 
best  methods  and  policies  to  be  pursued,  and  involves  questions 
of  an  administrative  and  engineering  nature.  Both  of  these  are 
complicated  on  account  of  the  right  of  the  farmer  to  receive  water 
from  the  system  at  the  exact  time  when  needed.  The  delivery  of 
water  therefore  must  be  given  first  consideration,  and  the  methods 
to  be  followed  in  making  deliveries,  and  in  maintaining  canals 
must  be  such  as  to  permit  operation  being  carried  on  continuously. 
To  the  farmer  who  is  dependent  upon  an  irrigation  supply  of  water 
for  his  success  and  livelihood  nothing  but  most  extraordinary  con- 
ditions are  sufficient  to  justify  the  cutting  off  of  this  supply  even 
for  a  single  day  at  the  time  when  it  is  required  for  the  growing  of 
crops. 

There  are  a  number  of  ways  by  which  water  for  agricultural 
purposes  is  distributed  to  lands.  These  are  to  a  limited  extent  the 
results  of  careful  experiment  and  scientific  investigations;  and  to  a 
greater  extent  the  outgrowth  of  the  crude  methods  used  by  the  first 
irrigators.  The  subject  of  best  handling  water  for  irrigation 
purposes  is  in  a  formative  state,  and  much  work  remains  to  be  done 
by  engineers  and  irrigation  managers  to  devise  means  best  suited  to 
each  particular  case.  In  order  to  improve  present  methods  it  is 
necessary  to  devise  others  better  suited  to  conditions,  and  also  to 
overcome  the  prejudice  which  commonly  exists  against  changes  in 
agricultural  operations. 

152 


OPERATION  AND  MAINTENANCE  153 

Generally  speaking  there  are  two  quite  distinct  systems  for  the 
distribution  of  water  to  lands,  viz.,  continuous  flow  and  periodic 
rotation.  In  order  to  consider  the  relative  merits  of  these  two 
systems  and  results  which  may  be  expected  from  each,  it  is  essential 
that  there  be  taken  into  account  the  conditions  of  the  soil  necessary 
for  the  growing  of  crops,  and  also  the  effect  of  water  continuously  and 
periodically  applied  to  it  in  producing  these  conditions. 

Continuous  Flow. — The  distribution  of  water  by  the  continuous 
flow  systems  assumes  that  a  stream  of  water  of  sufficient  quantity 
to  supply  the  needs  cf  a  given  area  is  kept  constantly  flowing  upon 
it.  Take  for  example  a  tract  of  say  50  acres,  and  let  us  assume  that 
it  is  desired  to  deliver  to  it  J  acre-foot  per  acre  during  a  period  of 
thirty  days.  The  volume  of  flow  required  to  deliver  this  quantity 

is  ''—  =  0.42  second-feet,  an  amount  usually  too   small  for 

economical  handling.  For  a  larger  or  smaller  area  a  proportionately 
larger  or  smaller  flow  is  required. 

The  distribution  of  water  by  continuous  flow  imitates  natural 
brooks  or  creeks.  It  was  the  system  naturally  adopted  in  the  early 
stages  of  irrigation  development  in  the  United  States.  The  smaller 
streams  were  diverted  from  their  channels  and  carried  out  in  long 
lines  of  canals,  which  were  divided  and  sub-divided,  each  carrying  a 
small  amount  of  water  to  its  respective  owner.  These  canals  were 
diverted  in  meandering  courses  across  the  fields  and  when  water  was 
not  required  on  the  lands  it  was  allowed  to  waste  back  into  the 
stream.  The  amount  of  water  which  was  delivered  to  a  given  area 
was  not  restricted  to  that  which  could  be  beneficially  used  and 
seldom  was  there  an  attempt  made  to  conserve  the  water  supply. 
When  water  was  plentiful  (as  was  the  case  during  the  flood  season) 
the  farmer  used  all  he  wanted  without  special  attention  being  given 
to  the  amount  which  should  be  applied  to  the  soil,  and  when  water 
was  scarce,  it  was  regarded  as  a  condition  for  which  no  one  was  to 
blame. 

As  irrigation  developed,  and  the  demands  for  water  increased,  it 
became  the  custom  to  limit  the  amount  which  each  man  might 
receive,  this  quantity  being  defined  by  a  stream  of  given  size.  From 
the  standpoint  of  the  farmer  who  desires  water  continuously  on  his 
land  so  that  irrigation  can  be  carried  on  at  any  time,  regardless  of 
whether  or  not  the  soil  is  in  proper  condition  for  irrigation,  such  a 
system  has  its  advantages.  Also  where  water  is  considered  as  a 
commodity  to  be  owned  by  an  individual  without  reference  to 


154      PRINCIPLES  OF  IRRIGATION  ENGINEERING 

whether  or  not  he  can  use  all,  or  a  part  of  it  to  advantage,  a  continu- 
ous flow  system  is  well  adapted  to  measuring  to  each  individual  that 
which  he  owns.  The  disadvantages  of  using  this  system  for  deliver- 
ing water  for  irrigation,  however,  are  many. 

In  order  that  the  soil  may  be  in  proper  condition  for  growing 
plants,  it  is  necessary  that  it  be  kept  supplied  with  moisture  to  the 
depth  penetrated  by  the  plant  roots.  It  must  not,  however,  be 
given  sufficient  water  to  become  saturated.  The  only  practical 
plan  of  obtaining  this  condition  is  to  apply  to  the  surface,  at  more  or 
less  regular  intervals,  a  sufficient  supply  of  water  to  moisten  the  soil 
to  the  required  depth.  The  moisture  thus  applied  is  held  in  suspen- 
sion by  the  soil  particles  until  taken  up  in  part  by  the  plant  roots 
and  in  part  by  evaporation  from  the  surface.  When  the  supply  of 
moisture  becomes  exhausted  so  that  the  plants  can  no  longer  find 
sufficient  to  sustain  them,  another  irrigation  is  required. 

By  the  continuous  flow  system  portions  of  the  land  over  which 
the  water  flows  become  saturated,  or  too  wet  for  plant  growth  to 
thrive  upon  it.  This  is  due  to  the  fact  that  the  soil  is  not  given  an 
opportunity  to  free  itself  from  the  excess  water  which  is  applied  to 
it.  In  addition  to  the  injury  of  lands  to  which  water  is  directly 
applied,  injury  to  those  adjacent  thereto  is  frequently  caused.  The 
result,  therefore,  is  ruinous  to  the  lands  of  the  irrigator  using  this 
system,  and  possibly  also  to  those  of  his  neighbor. 

The  quantity  of  water  required  for  the  irrigation  of  a  small  tract 
of  land,  as  for  example  the  ordinary  farm,  when  delivered  continu- 
ously produces  a  stream  too  small  to  permit  its  being  properly 
distributed.  This  is  especially  true  on  farms  the  soil  of  which 
absorbs  water  rapidly. 

In  general  it  may  be  said  that  the  continuous  flow  system  of 
delivery  is  wasteful  of  water,  detrimental  to  the  soil  and  not  well 
adapted  to  carrying  on  irrigation  operations. 

Periodic  Rotation. — This  method  of  delivering  water,  as  the 
name  implies,  is  to  supply  to  the  land  at  somewhat  regular  inter- 
vals the  amount  of  water  it  requires  to  keep  it  in  proper  condition 
for  plant  growth.  It  differs  from  the  continuous  flow  system 
previously  described  in  that  the  smaller  canals,  especially  those  to 
individual  water  users,  carry  water  during  only  a  portion  of  the  time. 
When  water  is  required  on  a  given  area  a  sufficient  quantity  is 
diverted  to  cover  it  in  the  shortest  possible  time,  and  the  supply 
is  then  passed  on  to  the  next  irrigator. 

The  advantages  of  this  method  may  be  enumerated  as  follows: 


OPERATION  AND  MAINTENANCE  155 

1.  It  permits  of  more  even  distribution  of  water,  since  the  lands 
adjacent  to  the  smaller  canals  do  not  become  saturated  as  is  the  case 
where  water  is  flowing  continuously  in  them. 

2.  The  soil  is  kept  in  better  condition  by  being  allowed  to  become 
warmed  and  aerated  during  the  period  when  water  is  not  applied 
to  it. 

3.  It  permits  of  more  economic  irrigation,  since  the  farmer  re- 
ceives his  supply  in  sufficient  quantity  to  permit  its  being  carried 
quickly  over  the  lands. 

4.  The  system  is  economical  in  the  use  of  water,  due  to  the  fact 
that  unnecessary  waste  and  losses  from  the  smaller  canals  is  avoided, 
and  water  is  delivered  only  when  and  where  it  is  needed. 

The  delivery  of  water  by  periodic  rotation  imitates  on  a  small 
scale  the  efforts  now  being  made  to  conserve  the  water  supply  of 
a  given  stream  or  watershed,  so  as  to  make  it  serve  the  largest  possible 
area.  To  accomplish  this  the  water  is  held  in  storage  and  diverted 
to  the  streams  or  canals  only  when  actually  required  for  irrigation. 

The  partial  drying  of  the  soil  after  one  irrigation  and  before  the 
next  is  applied  permits  greater  freedom  of  cultivation,  which  serves 
to  reduce  the  quantity  of  water  required.  Thorough  cultivation, 
to  a  certain  degree,  can  be  made  to  supplement  a  deficiency  in 
water  supply,  by  reducing  evaporation  from  the  surface. 

The  period  of  rotation  in  any  particular  case  will  depend  upon 
climatic  conditions,  character  of  soil,  and  kind  of  crops  raised. 
The  essential  requirement  is  that  water  be  applied  to  the  soil  at 
periodic  intervals  when  required. 

Length  of  Irrigation  Season. — The  actual  time  during  the  year 
that  irrigation  is  required,  or  the  irrigation  season,  as  it  is  commonly 
called,  varies  greatly  in  different  localities.  It  depends  primarily 
on  the  climate  in  regard  to  temperature  and  seasonal  rainfall. 

In  the  regions  where  long  cold  winters  prevail  the  irrigation 
season  is  necessarily  limited  to  the  late  spring  and  summer  months 
and  no  water  should  be  placed  upon  the  lands  until  they  have  been 
warmed  sufficiently  by  the  approach  of  summer  to  stimulate  plant 
growth.  In  a  climate  having  a  more  or  less  definite  season  of  rain- 
fall, during  the  spring  or  early  summer  irrigation  is  frequently  not 
needed  until  the  rainy  season  is  passed. 

Where  the  climate  is  sufficiently  mild  to  allow  crops  to  grow 
during  the  winter  season,  as  is  the  case  in  some  of  the  arid  regions 
of  the  southwest,  irrigation  may  be  required  throughout  the  entire 
year.  Ordinarily,  in  this  section  the  natural  rainfall  is  too 


156      PRINCIPLES  OF  IRRIGATION  ENGINEERING 

small  or  too  erratic  in  character  to  take  the  place  of  a  single 
irrigation. 

During  the  irrigation  or  growing  season  water  sufficient  for  the 
plants  should  be  applied  to  the  soils;  as  soon  as  the  growing  season 
is  over  it  should  be  shut  out  of  the  canal  system  so  that  the  soil 
may  become  dry  and  aerated.  With  the  approach  of  spring  it  is 
then  warmed  and  early  planting  may  result.  If  irrigation  is 
practised  during  the  non-growing  season  the  presence  of  the  excess 
moisture  in  the  soil  renders  it  less  porous  and  less  responsive  to  the 
sun's  action. 

In  the  more  northern  and  colder  portions  of  the  United  States 
the  irrigation  season  extends  from  about  the  ist  of  May  to  the  ist 
of  October.  Going  southward  the  season  gradually  lengthens  until, 
as  above  stated,  it  is  continuous  throughout  the  year. 

The  proper  time  to  begin  irrigation  in  the  spring  and  to  discon- 
tinue delivering  water  in  the  fall  are  questions  of  importance  in 
operation  and  maintenance  work.  It  may  happen  that  the  bene- 
fits of  late  fall  irrigation  to  one  season's  crop  may  be  more  than 
offset  by  the  damage  it  does  in  retarding  the  first  crop  of  the  follow- 
ing year.  No  definite  rule  can  be  formulated  as  to  when  irriga- 
tion shall  be  begun  or  ended.  A  careful  study  of  soil  conditions 
and  the  results  that  may  be  accomplished  is  the  only  guide. 

Frequency  of  Irrigation. — There  is  a  wide  variation  in  the  time 
which  may  elapse  between  irrigations.  It  depends  upon  the  climate, 
soil  and  character  of  crops  raised.  Coarse,  porous  soils,  such  fof 
example  as  sands  or  gravels,  hold  but  little  moisture  in  suspension. 
In  a  climate  where  the  rate  of  evaporation  is  high,  the  moisture  near 
the  surface  is  rapidly  exhausted.  Shallow  plants  on  soils  of  this 
kind  require  irrigation  at  intervals  of  a  few  days.  By  some  farmers 
it  is  held  that  root  crops  planted  in  porous  soil  require  water  at 
intervals  of  from  one  to  two  days.  Experience  has  shown  that 
that  is  excessive  and  that  better  results  can  be  obtained  with  less 
frequent  irrigation. 

For  alfalfa,  the  stable  forage  crop  of  the  west,  it  is  sufficient  in  the 
more  northern  localities  to  apply  water  once  for  each  cutting. 
Further  south  in  the  warmer  regions  each  crop  is  ordinarily  irrigated 
twice  or  more,  water  being  applied  in  some  cases  every  ten  days 
during  the  warmer  months. 

It  is  evident  that  for  complete  success  the  frequency  of  irrigation 
must  be  adapted  to  the  character  of  crops,  time  of  planting,  etc. 
The  schedule  for  supplying  water  to  the  fields  in  the  district  must  be 


OPERATION  AND  MAINTENANCE 


157 


arranged  with  a  full  knowledge  of  the  crops  growing  in  that  district. 
In  other  words,  there  must  be  complete  cooperation  and  good  busi- 
ness management  between  irrigation  managers  and  farmers,  acting 
individually  or  in  groups.  If  one  crop  is  of  such  a  character  or  is  so 
planted  as  to  require  irrigation  during  a  certain  week,  the  schedule 
for  water  deliveries  must  be  arranged  accordingly  or  the  crop  will 
suffer.  If  the  crops  are  of  such  nature  as  to  require  daily  application 
of  water,  some  special  provisions  must  be  made  for  supplying  them. 
In  other  words,  it  should  be  remembered  that  the  primary  purpose 
of  irrigation  is  to  supply  crops  with  water,  and  no  rules  relative  to 
times  of  delivery  should  be  so  iron-clad  as  to  interfere  with  this 
purpose. 

An  example  of  one  of  the  schedules  actually  used  by  the  United 
States  Reclamation  for  the  operation  of  the  Williston  pumping 
plant,  North  Dakota,  is  as  follows: 

"The  operation  of  the  Williston  canal  system  for  the  season  of  1911, 
will  begin  June  4.  In  order  to  secure  economical  and  uniform  operation, 
deliveries  of  water  from  the  different  canals  will  be  restricted  in  so  far 
as  practicable  to  the  dates  listed  below,  water  to  be  delivered  in  rota- 
tion, beginning  at  the  lower  end  of  the  system,  running  continuously 
until  irrigation  is  completed,  and  in  such  quantities  as  can  be  most 
advantageously  handled. 

"Water  will  be  delivered  from: 


Canals  B  &  S,  and  Canal  A,  South  of 

Station  No.  2. 
June  4  to  June  13 
June  24  to  July  3 
July  14  to  July  23 
August  3  to  August  12 


Canals  D  &  E,  and  Canal  A,  North  of 

Station  No.  2. 
June  14  to  June  23 
July  4  to  July  13 
July  24  to  August  2 
August  13  to  August  22 


"Application  cards,  stating  whether  water  is  desired  during  a  ten-day 
run,  must  be  mailed  and  received  at  the  project  office  two  days  prior  to 
the  beginning  of  each  ten-day  run,  and  the  water-user  will  be  notified 
in  advance  when  delivery  will  commence.  If  it  is  not  convenient  to 
take  water  at  the  time  designated,  it  will  be  necessary  to  wait  approxi- 
mately twenty  days  until  the  next  ten-day  run." 

Duty  of  Water. — The  term  "  duty  of  water  "  is  a  form  of  expression 
for  the  quantity  of  water  required  for  irrigation.  It  is  sometimes 
expressed  as  the  area  which  a  continuous  flow  of  a  given  amount 
will  irrigate.  For  example,  it  may  be  said  that  the  duty  of  water  is 
i  second-foot  for  each  100  acres,  meaning  that  i  second-foot  con- 
tinuous flow  will  irrigate  100  acres.  Another  way  of  expressing 
duty  of  water  is  by  means  of  the  depth  applied  to  the  land,  that  is, 
the  number  of  acre-feet  per  acre  for  a  given  period  of  time,  for 


158      PRINCIPLES  OF  IRRIGATION  ENGINEERING 

example,  a  month  or  a  year.  The  larger  the  area  irrigated  by  a 
given  quantity  the  higher  the  duty  of  water  is  said  to  be. 

The  determination  of  the  proper  amount  of  water  to  be  used  in 
irrigation  is  perhaps  the  most  difficult  question  to  be  solved  by  the 
farmer  and  irrigation  manager.  It  is  affected  by  the  kind  of  crop, 
character  of  soil,  the  rate  of  evaporation  in  the  particular  locality 
and  also  the  skill  of  the  irrigator.  When  water  is  applied  to  the 
soil  a  part  of  it  is  taken  up  by  the  growing  plants,  a  part  is  consumed 
by  evaporation  from  the  surface,  and  a  varying  amount  is  lost  by 
being  carried  downward  through  the  sub-soil  and  eventually  returned 
as  drainage  water  to  the  streams  below. 

It  is  estimated  that  to  produce  i  Ib.  of  dry  vegetable  matter 
requires  from  300  to  500  Ib.  of  water.  Using  this  as  a  basis,  it  would 
require  from  about  2  1/2  to  4  1/2  in.  in  depth  over  the  land  to  produce 
i  ton  of  dry  matter  per  acre.  It  is  of  course  impracticable  to  apply 
the  theoretically  exact  amount  of  water  to  the  land  on  account  of 
evaporation  and  other  losses  which  cannot  be  measured. 

It  is  ordinarily  impossible  to  irrigate  lands  without  some  water 
being  lost  by  its  penetrating  below  the  zone  of  the  plant  roots. 
Various  estimates  of  the  amount  of  such  losses  have  been  made, 
but  on  account  of  the  varying  conditions  met  with  it  is  impossible 
to  apply  them  with  safety  to  any  particular  case.  It  is  believed 
that  the  loss  by  percolation  below  the  plant  root  zone  should  not 
exceed  25  per  cent,  of  the  total  quantity  placed  on  the  land,  and 
that  under  careful  irrigation  on  average  soils  it  may  be  made  much 
less  than  this. 

The  determination  of  the  proper  amount  of  water  to  use,  as  a 
practical  question,  can  best  be  solved  by  observations  on  the  condition 
of  the  soil  under  varying  water  deliveries.  In  doing  this  care  should 
be  taken  to  see  that  more  water  is  not  applied  at  any  one  irrigation 
than  the  soil  can  absorb  and  hold  in  suspension. 

Investigations  made  during  the  past  few  years  seem  to  show  that 
in  most  irrigated  sections  where  the  quantity  of  water  is  not  limited, 
more  is  used  than  is  necessary.  The  result  of  this  excess  use  is  a 
decrease  rather  than  an  increase  in  crop  production.  It  also  has 
the  effect  of  impoverishing  the  land  by  leaching  out  valuable  con- 
stituents or  rendering  them  waterlogged  or  alkaline. 

On  the  projects  of  the  United  States  Reclamation  Service  the 
amount  of  water  required  for  a  season's  irrigation  varies  according 
to  the  best  data  available  from  1.5  to  3.5  acre-feet  per  acre,  the 
average  being  about  2  acre-feet  per  acre. 


OPERATION  AND  MAINTENANCE  159 

In  addition  to  the  losses  due  tc  the  application  of  too  much  water 
to  the  soil  there  are  also  frequently  large  losses  in  transportation. 
Water  is  carried  for  the  most  part  not  in  tight  pipes  or  impervious 
conduits,  but  in  open  ditches  built  through  more  or  less  porous  soils, 
and  distributed  by  furrows  passing  often  through  sand  or  gravel 
areas  in  which  a  small  stream  may  completely  disappear. 

The  quantity  which  must  be  delivered  to  canals  is,  thus,  greatly 
in  excess  of  the  quantity  theoretically  needed  on  the  land.  To  carry 
this  amount  to  a  point  where  needed,  it  is  necessary  to  send  it  in 
considerable  volume,  or  "head"  so  that  it  can  flow  quickly  across 
the  more  porous  places.  The  larger  the  head  of  water  in  a  canal  the 
greater  the  velocity  and  the  smaller  the  percentage  of  loss  due  to 
seepage. 

As  seepage  losses  only  occur  from  the  wetted  perimeter  of  a  ditch 
or  furrow,  it  is  obvious  that  the  quantity  of  water  can  be  greatly  in- 
creased in  the  canal  without  notably  adding  to  this  wetted  perimeter 
and  consequent  loss;  also,  if  the  amount  needed  to  irrigate  a  field  can 
be  applied  in  half  the  usual  time,  it  is  apparent  that  the  losses  from 
this  source  will  be  reduced.  Quickness  in  applying  water  results  in 
economy,  and  the  quantity  needed  is  dependent  largely  on  the  skill 
and  rapidity  of  application  of  the  water.  This  in  turn  is  governed 
to  a  certain  extent  by  the  size  and  location  of  the  canal  and  structures, 
slope  of  ground  and  character  of  soil. 

Measurements  of  losses  by  seepage  and  evaporation  indicate  that 
these  losses  in  some  cases  are  very  great  and  that  one  of  the  most 
important  steps  for  securing  economy  in  the  use  of  water  is  in 
reducing  these  losses.  As  long  as  open  canals  are  used  there  must 
be  a  steady  loss  through  evaporation.  The  expense  of  reducing 
these  losses  by  covering  the  canals  or  putting  the  water  in  closed 
pipes  will  probably  be  far  in  excess  of  the  value  of  the  water  under 
present  conditions,  but  the  seepage  losses  from  the  sides  and 
bottoms  of  the  canals  should  be  reduced  wherever  practicable,  as 
these  are  frequently  of  injury,  not  merely  in  the  loss  of  the  water 
itself  but  in  the  seeping  and  rendering  swampy  or  alkaline  of  lands 
even  at  considerable  distance  from  the  canals. 

Measurements  of  losses  have  been  made  on  various  canals  giving 
results  of  which  the  following  are  examples: 

From  the  feed  canal  on  the  Umatilla  project,  Ore.,  the  loss  by 
seepage  and  evaporation  in  the  season  of  1909  was  13.2  per  cent,  of 
the  amount  taken  into  the  canal,  this  begin  equivalent  to  396  acre- 
feet  per  mile  of  canal  or  98  acre-feet  per  acre  of  wetted  area  of  canal. 


160     PRINCIPLES    OF  IRRIGATION  ENGINEERING 

On  the  distributing  system  of  the  same  project  the  losses  by  seepage 
and  evaporation  amounted  to  41.4  per  cent,  of  the  amount  taken 
from  the  reservoir. 

On  the  Minidoka  project,  Idaho,  the  loss  between  the  amount 
taken  into  the  main  canal  and  turned  to  the  sub-laterals  was  on  the 
north  side  gravity  system  29  per  cent,  and  on  the  south  side  47  per 
cent. 

On  the  North  Platte  project,  Wyoming  and  Nebraska,  the  losses 
on  the  main  canal  were  from  4  to  14  per  cent,  and  on  the  laterals 
from  5  to  39  per  cent.,  dependent  on  the  character  of  soil  traversed. 
The  average  elsewhere  was  about  18  per  cent. 

On  the  Truckee-Carson  project,  Nevada,  the  average  losses  on 
a  portion  of  the  distributing  system  were  20.7  per  cent.,  and  on  the 
Okanogan  project  in  Washington  from  the  main  canal  and  distribut- 
ing system  were  45  per  cent. 

An  average  series  of  measurements  made  on  the  Yakima  pro- 
ject, Washington,  in  1910,  showed  that  of  the  total  amount  of 
water  taken  into  the  main  canal  and  branches  22.4  per  cent,  was 
lost,  of  that  taken  into  the  lateral  system  3  2  per  cent,  was  lost,  and 
of  that  taken  into  the  sub-lateral  system  1 5  per  cent,  was  lost. 

Measurement  of  Water  Used. — Measurements  of  water  used  in 
agriculture  are  as  essential  to  the  proper  conduct  of  a  system  of 
irrigation  of  any  considerable  size  as  are  measurements  of  the 
supplies  sold  by  a  produce  dealer.  Without  accurate  measurements 
and  records  confusion  and  loss  quickly  result.  In  the  case  of  a  very 
small  system,  there  is  obviously  not  the  same  necessity  for  making 
measurements  any  more  than  there  is  of  the  individual  householder 
carefully  weighing  out  the  supplies  for  current  use.  But  where 
hundreds  of  individuals  are  concerned,  and  where  apparently  in- 
significant errors  may  accumulate  in  a  large  general  loss,  there 
common  sense  and  business  rules  demand  accuracy  and  system  in 
management  and  in  accounting. 

In  the  accompanying  Plate  X,  Figs.  C  and  D,  are  shown  measur- 
ing devices  as  used  on  some  of  the  irrigation  canals.  At  Fig.  C  is  a 
weir  and  self-registering  gage  such  as  has  been  installed  on  the 
Williston  project,  North  Dakota,  where  water  is  pumped  from  the 
Missouri  River.  Fig.  D  is  a  view  of  an  automatic  gage  such  as  is 
used  at  one  of  the  stations  on  the  Laramie  River  in  Colorado. 

The  amount  of  water  held,  or  turned  out  of  the  reservoirs,  or 
received  at  the  head  of  a  system,  must  be  recorded  from  day  to 
day.  Following  down  the  main  trunk  line,  there  should  also  be 


OPERATION  AND  MAINTENANCE  161 

measurements  at  several  points  in  order  to  check  losses  through 
seepage,  and  to  verify  the  measurement  at  the  head.  As  the  water 
is  turned  out  in  each  of  the  principal  branches,  it  should  again  be 
measured  so  that  for  each  district,  or  division  of  the  canal  system, 
the  amount  of  water  received  each  day  should  be  known  and  losses 
again  checked.  Finally,  the  amount  measured  to  each  farm  or  group 
of  farms,  together  with  the  time  of  delivery,  must  be  recorded  in 
order  to  have  accurate  data  to  settle  the  innumerable  disputes 
which  may  arise. 

The  measurements  of  larger  quantities  of  water  discharged  from 
a  reservoir  or  received  into  the  head  of  a  canal  are  usually  made 
by  some  form  of  weir  or  submerged  orifice.  Where  the  latter  is 
used  it  is  usually  calibrated  by  means  of  a  current  meter.  The 
width  and  depth  of  the  stream  is  obtained  by  direct  measurement 
and  the  velocity  of  all  parts  by  any  one  of  a  considerable  number 
of  devices  on  the  market,  most  of  these  consisting  of  a  rotating 
wheel,  the  speed  of  which  varies  with  the  velocity  of  flow.  All 
such  instruments  must  be  rated,  that  is,  the  ratio  between  the  speed 
of  the  water  and  the  number  of  turns  of  the  wheel  per  second  being 
determined  by  direct  measurement  for  each  instrument. 

Wherever  there  is  ample  fall,  it  is  preferable  to  make  measurements 
by  means  of  a  weir,  following  the  conventional  forms,  and  using 
tables  computed  from  formulae  based  on  experimental  data  giving 
the  ratio  of  water  flowing  to  a  depth  on  the  weir. 

The  measurement  of  these  large  volumes  of  water  is  relatively 
simple,  and  follows  well-established  practices.  The  greatest  diffi- 
culties, however,  are  encountered  in  measuring  economically  the 
smaller  quantity  of  water  directly  to  the  field  of  the  farmer.  There 
are  a  great  many  devices  for  this  purpose,  but  those  which  yield 
fairly  accurate  results  are  quite  expensive.  The  problem  of  in- 
troducing and  using  these  on  an  old  canal  system  is  similar  to  that 
of  attaching  meters  to  the  service  pipes  in  a  city.  Theoretically 
this  should  always  be  done,  but  practically  the  cost  of  the  instru- 
ments and  care  required  has  been  a  great  obstacle.  In  the  same 
way,  the  cost  of  procuring,  installing,  and  maintaining  a  suitable 
measuring  device  or  module  at  each  farm  has  been  so  great  as  to 
be  almost  prohibitory  for  the  ordinary  irrigation  system. 

The  devices  used  for  measuring  water  to  the  farmers  have  usually 
been  somewhat  crude,  being  manufactured  locally,  and  consisting 
of  measuring  boxes  made  of  plank  or  boards,  in  which  by  adjusting 
small  wooden,  or  iron  gates,  the  water  is  allowed  to  escape  through 


162      PRINCIPLES  OF  IRRIGATION  ENGINEERING 

a  rectangular  orifice.  Where  there  is  sufficient  head,  it  is  sometimes 
allowed  to  flow  over  a  small  weir,  and  for  each  of  these  weirs  a  table 
is  made  to  show  the  quantity  of  water  discharged.  Where  it  is  not 
possible  to  provide  a  fall  or  drop  in  the  water  from  the  canal  or 
lateral  to  the  field,  the  water  is  sometimes  conducted  in  a  wooden 
flume  on  a  nearly  level  grade,  in  which  measurements  are 
made  of  the  width  and  depth,  and  the  velocity  ascertained  by  small 
floats,  or  by  current  meters  devised  for  the  purpose.  In  this  latter 
case  a  table  is  prepared  showing  the  quantity  of  water  flowing  for 
different  depths  in  the  flume. 

Human  Element. — In  the  practical  working  out  of  an  irrigation 
system,  and  in  the  distribution  of  water  to  the  land  the  most 
serious  consideration  is  not  the  engineering  or  mechanical  difficulties, 
but  those  which  arise  from  having  to  deal  with  considerable  numbers 
of  men  of  more  or  less  limited  education,  coming  from  all  parts  of 
the  world,  frequently  with  strong  native  prejudices,  or  with  experi- 
ence under  conditions  entirely  different  from  those  had  under 
successful  irrigation.  Many  of  these  men  must  unlearn  much 
which  they  regard  as  of  first  importance.  Others  have  none  of 
the  qualities  which  lead  to  success  in  farming.  Some  are  of  a  roving 
disposition  who  are  attracted  by  the  novelty  of  a  change  in  vocation 
or  by  the  glowing  advertisements  of  land  speculators. 

Under  these  conditions  factions  arise,  and  under  even  the  most 
patient  and  tactful  management  there  are  always  a .  number  of 
farmers  or  settlers  who  attribute  their  lack  of  success  not  to  them- 
selves but  to  the  operation  and  management  of  the  irrigation  works. 

Since  the  salary  paid  to  a  superintendent  or  manager  of  a  system 
is  not  always  sufficient  to  attract  and  hold  a  diplomat  of  high  order 
especially  one  who  also  possesses  the  skill  of  an  engineer  and  the 
practical  knowledge  of  an  experienced  farmer,  it  from  necessity 
follows  that  there  is  more  or  less  friction  in  the  management.  The 
man  who  can  handle  a  large  irrigation  enterprise  without  complaints 
from  the  farmers  can  readily  obtain  a  salary  elsewhere  far  too  great 
to  justify  his  remaining  on  an  irrigation  work! 

This  condition  must  be  borne  in  mind  at  all  times  in  the  opera- 
tion and  management  of  any  work  of  this  kind,  which  has  to  do 
with  the  untrained  men  working  under  pioneer  conditions.  With- 
out any  organization  or  means  of  control — each  man  is  free  to  act 
as  he  pleases — planting  his  own  crops  in  his  own  way,  and  at  his 
own  time.  Under  these  circumstances,  no  system,  however  well 
planned,  can  meet  the  individual  demands  of  the  farmers.  There 


OPERATION  AND  MAINTENANCE  163 

must  always  be  criticism  and  complaints  which  require  the  exercise 
of  unusual  patience  and  forbearance  on  the  part  of  the  management. 
It  must  not  be  supposed  that  because  complaints  are  continually 
made,  that  the  system  is  badly  planned  or  poorly  operated.  The 
engineer  himself  must  clearly  distinguish  between  those  criticisms 
which  are  important,  or  vital,  and  those  which  arise  simply  from 
having  to  do  with  a  mass  of  humanity  not  yet  educated  by  experi- 
ence in  that  particular  climate,  soil,  and  surrounding. 

Maintenance. — The  maintenance  of  an  irrigation  system  is  theo- 
retically distinct  from  the  operation,  but  practically  is  very  inti- 
mately connected  with  it,  as  the  maintenance  must  be  carried  on 
in  the  same  place  and  often  at  the  same  time  with  the  operation. 

Theoretically  a  canal  should  be  operated  during  the  crop  season 
by  a  force  proportioned  to  the  number  of  distributions  to  be  made 
and  the  number  of  miles  of  canals  and  laterals  to  be  operated,  and 
this  force  should  report  all  defects,  accidents,  or  worn-out  apparatus, 
and  as  a  result  of  this,  the  maintenance  to  be  taken  up  as  a  sepa- 
rate item.  As  a  matter  of  fact,  however,  it  is  economical  and  often- 
times necessary  for  the  operating  force  to  make  many  of  these  re- 
pairs or  adjustments  when  they  are  discovered,  although  it  is  de- 
sirable to  have  what  is  sometimes  called  in  railroad  work  "an  extra 
gang"  ready  to  go  to  any  point  to  repair  or  renew  structures  needing 
attention. 

The  successful  operation  is  dependent  not  only  upon  proper 
construction  originally,  but  also  upon  immediate  and  effective 
maintenance  of  all  of  the  structures.  There  is  more  or  less  deprecia- 
tion at  all  times,  and  the  gradual  weakening  of  one  part  or  another 
is  sometimes  of  such  a  nature  that  the  work  can  be  done  at  almost 
any  time  during  several  months,  or  even  years. 

Successful  and  economical  maintenance  depends  upon  having 
accurate  knowledge  of  the  character  and  extent  of  the  gradual  as 
well  as  of  the  accidental  depreciation,  and  of  organizing  the  work 
so  that  immediate  attention  is  given  to  breaks  or  critical  places. 
At  other  times  the  men  should  be  employed  in  improving  the  prop- 
erty where  wear  or  decay  is  taking  place,  so  that  the  maintenance 
cost  may  be  kept  at  a  fairly  uniform  rate. 

It  occasionally  happens  that  a  careful  and  competent  superintend- 
ent who  has  thoroughly  understood  the  work,  and  who  for  the  good 
of  the  system  has  been  forced  from  year  to  year  to  make  certain 
expenditures  in  maintenance,  is  replaced  by  a  man  who  desires  to 
make  a  record  for  economy.  The  new  management  can  cut  down 


164     PRINCIPLES  OF  IRRIGATION  ENGINEERING 

the  maintenance  cost  notably  for  the  time,  but  the  inevitable  result 
happens  that  the  entire  property  depreciates  in  value,  and  in  the 
course  of  a  year  or  several  years,  breaks  or  accidents  occur  one  after 
the  other,  the  total  cost  of  these  being  far  greater  than  the  apparent 
saving  previously  made.  In  comparing  the  cost  of  maintenance  in 
different  years  or  different  systems,  this  fact  must  be  always  borne 
in  mind,  and  careful  analysis  made  to  ascertain  whether  the  mainte- 
nance has  been  careful  and  complete,  or  whether  it  has  neglected 
some  essential  point,  and  exposed  the  system  to  larger  loss. 

Priming. — The  expense  of  maintenance  is  materially  affected 
by  the  care  and  skill  shown  in  priming  the  canal,  especially  in  skill- 
fully bringing  the  water  against  all  new  works.  Large  amounts 
of  money  have  been  lost  by  lack  of  care  in  this  regard,  by  attempting 
to  use  canals  before  they  have  been  properly  primed. 

In  the  case  of  new  banks,  especially  those  which  have  not  been 
thoroughly  wet  and  compacted  in  construction,  the  water  should 
be  brought  against  them  very  slowly,  being  raised  from  day  to  day, 
and  carefully  watched.  In  the  case  of  long  sections  of  new  or  re- 
cently repaired  canal,  it  may  be  necessary  to  provide  temporary  dams 
of  timber  and  boards,  or  of  sacks  of  earth,  by  means  of  which  the 
water  level  can  be  raised  a  few  inches  at  a  time,  watching  carefully 
all  possible  locations  where  there  may  be  signs  of  weakness,  and 
reducing  the  water  level  at  once,  if  leaks  are  discovered;  at  the  same 
time  puddling  the  points  where  there  appear  to  be  holes  or  pervious 
places.  The  points  of  greatest  danger  are  at  the  juncture  between 
the  earth  and  the  concrete,  masonry,  or  wooden  structures.  Here 
extreme  care  must  be  used  in  bringing  water  against  the  points 
of  junction,  raising  it  with  great  slowness  and  with  devices  such 
that  the  level  can  be  immediately  reduced  if  there  is  any  tendency 
to  break  through. 

Care  of  Banks. — The  maintenance  of  earthworks  is  a  matter 
requiring  continual  vigilance.  Nature  is  perpetually  endeavoring 
to  level  down  all  surface  elevations  of  this  character,  and  most  of  the 
ordinary  operations  of  men  aid  this  leveling.  Cattle  tramping  over 
the  earth  tend  to  loosen  it,  permitting  the  winds  to  blow  it  away,  or 
cause  it  to  roll  down  the  slopes. 

The  canal  banks  frequently  afford  convenient  roads  and  in  many 
instances  it  is  a  matter  of  necessity  for  the  men  in  charge  of  the  work 
to  travel  on  the  canal  banks.  This  has  a  certain  advantage  in 
compacting  the  soil,  but  it  tends  to  make  paths,  or  ruts,  which  catch 
the  rain-water.  If  the  banks  are  to  be  used  for  roadways,  they 


OPERATION  AND  MAINTENANCE  165 

should  be  made  higher  and  wider  than  is  required  for  canal  purposes 
only. 

The  banks  should  be  kept  as  symmetrical  as  possible,  slightly 
crowned  on  top  and  sown  with  grass-seed,  or  the  growth  of  grass 
and  clover  encouraged.  Until  plants  of  this  character  have  taken 
possession,  the  larger  and  more  injurious  weeds  rapidly  spread,  and 
it  is  necessary  occasionally  to  cut  these,  especially  those  which  break 
off  when  dry  and  blow  into  the  canal. 

In  the  warmer  climates  Bermuda  grass  has  been  tried  and  while 
this  is  very  successful  in  protecting  the  banks  it  becomes  a  serious 
menace  to  the  fields  of  the  farmer  under  conditions  where  the  frost 
is  not  sufficiently  heavy  to  kill  it  during  the  winter. 

Cleaning  Canals. — It  is  necessary  to  clean  most  canals  annually 
or  oftener  not  only  to  remove  the  accumulated  silt  but  under  some 
conditions  to  get  rid  of  the  aquatic  plants  or  moss,  the  latter  term 
including  a  great  variety  of  growth. 

This  so-called  "  moss  "growing  in  the  bottom  of  the  canal  forces 
the  water  to  be  carried  above  the  normal  level,  presenting  fresh 
surfaces  of  the  canal  bank  to  the  water  and  increasing  the  losses  by 
percolation,  also  the  danger  of  breaks  by  the  water  finding  its  way 
into  holes  or  points  of  weakness  left  by  burrowing  animals. 

The  destruction  of  this  moss  is  a  serious  problem  in  some  locali- 
ties; the  attempt  has  been  made  to  prevent  its  growth  by  lin- 
ing the  canal  with  cement,  but  this  is  not  wholly  effective  as  shown 
by  the  fact  that  on  the  Twin  Falls  Canal  in  Idaho  the  only  place 
reported  as  having  trouble  with  moss  is  in  a  concrete-lined  section 
where  the  velocity  is  stated  to  be  as  high  as  10  ft.  per  second. 

This  moss  does  not  grow  rapidly  in  the  shade  but  is  troublesome 
where  the  water  is  clear  and  exposed  to  bright  sunlight.  In  some 
localities  cottonwood  or  other  quick-growing  trees  are  planted  alorg 
the  canal  in  order  to  provide  a  shade  in  the  hopes  that  within  two  or 
three  years  the  shadows  from  the  trees  will  be  sufficient  to  practically 
prevent  or  to  a  large  extent  control  the  growth  of  moss. 

Mowing  machines  to  be  drawn  through  the  canal  by  horses  walking 
either  in  the  water  or  on  the  banks  have  been  devised.  These  cut 
the  aquatic  plants  while  the  canal  is  full  of  water  or  in  operation 
and  as  the  material  rises  and  floats  away,  it  is  caught  and  pulled 
out  upon  the  bank.  Heavy  chains  are  also  drawn  along  the  canal 
bottom  tearing  loose  the  plants  or  in  some  instances  a  metal  band 
with  teeth  or  "moss  saw"  is  used  to  cut  or  tear  the  aquatic  growth. 
Wherever  it  is  practicable  to  rotate  or  alternate  in  the  use  of  water, 


166      PRINCIPLES  OF  IRRIGATION  ENGINEERING 

the  canal  bed  is  left  dry  a  few  days,  so  that  the  sun  will  destroy  the 
weeds;  but  on  the  main  canal  this  is  not  possible. 

The  vegetable  growth  in  irrigating  canals  include  many  species  of 
algae  representing  such  genera  as  Spirogyra,  Stichococcus,  Micro- 
spora,  Ulothrix,  etc.,  occurring  in  flowing  water  of  canals.  In  still 
water  these  may  usually  be  eradicated  with  little  or  no  difficulty  by 
the  application  of  a  small  quantity  of  copper  sulphate.  The 
different  species  vary  greatly  in  their  susceptibility  to  this  poison; 
some  species  are  readily  killed  by  an  exposure  of  two  to  four  hours 
to  a  solution  of  one  part  of  copper  sulphate  to  twenty  million  parts 
of  water,  while  others  resist  for  several  hours  a  concentration  of  one 
part  of  copper  sulphate  to  one  million  parts  of  water.  In  addition 
to  these  susceptible  algae  other  plants  such  as  Potamogeton,  Chara, 
etc.,  sometimes  appear  in  canals,  and  are  too  resistant  to  the  action 
of  chemical  agents  to  be  eradicated  by  such  means. 

Organization  for  Operation  and  Maintenance. — The  organization 
for  operation  and  maintenance  depends  largely  upon  the  size  of  the 
system  and  its  complications.  ,  A  small  system  can  be  operated  by 
a  very  few  men,  as  is  the  case  with  a  small  railroad,  where  it  makes 
little  difference  whether  absolute  accuracy  as  to  time  and  service  is 
observed.  With  the  large  irrigation  system,  however,  embracing 
thousands  of  farms,  where  every  small  error  in  judgment  may  result  in 
losses  to  hundreds  of  individuals,  far  greater  care  proportionally  must 
be  given  to  a  system,  and  the  expense  is  correspondingly  increased, 
the  organization  being  more  highly  specialized  and  adapted  to  the 
greater  demands  made  upon  it. 

The  object  of  this  organization,  and  in  fact  of  the  whole  works, 
is  to  deliver  water  promptly  and  in  necessary  quantities.  Reliable 
service  is  of  the  highest  importance — far  more  than  cheapness  of 
operation.  With  good  management  the  crop  returns  are  so  large, 
and  with  poor  management  so  disappointing,  that  the  irrigators 
have  less  concern  about  the  cost  than  they  have  about  the  efficiency. 

At  the  head  of  the  organization  must  necessarily  be  the  manager, 
who  must  oversee  the  general  system,  decide  all  questions  in  ac- 
cordance with  the  laws  and  regulations,  and  settle  the  innumerable 
controversies  which  are  inseparable  with  delivery  of  water  through 
open  channels.  Under  the  project  manager  are  usually  two  or 
more  superintendents,  who  in  turn  have  oversight  of  a  sufficient 
number  of  water  masters  or  canal  riders  to  enable  the  entire  sys- 
tem, including  hundreds  of  miles  of  main  and  branch  canals  to  be 
traversed  once  or  twice  each  day. 


OPERATION  AND  MAINTENANCE  167 

In  an  irrigation  project  with  farms  of  ordinary  size  the  irrigated 
acreage  in  each  being  from  40  to  60  acres  or  more,  one  canal  rider 
is  required  for  about  3,000  acres.  If  every  delivery  is  to  be  visited 
each  day  the  number  of  canal  riders  will  be  materially  increased 
and  in  case  the  holdings  of  80  or  160  acres  each  the  number  can  be 
reduced. 

The  wages  paid  to  canal  riders  generally  range  from  $75  to  $80 
a  month  and  may  go  as  high  as  $90  or  $95.  In  most  cases  local  men 
are  employed,  the  more  important  men  being  kept  throughout 
the  year  and  the  others  for  six  months  or  during  the  irrigation 
season.  Each  canal  rider  is  required  usually  to  furnish  his  own 
horse  and  has  frequent  need  of  an  additional  animal  to  allow  suitable 
rest,  as  the  daily  average  ride  is  from  20  to  25  miles.  The  water 
masters  are  paid  usually  $125  to  $150  a  month  and  supervise  eight 
or  ten  or  more  canal  riders.  There  is  also  a  clerical  force  the  size 
of  which  is  dependent  upon  the  detail  with  which  the  records  are 
kept. 

Records. — Accurate  records  are  as  essential  in  the  proper  operation 
and  maintenance  of  a  system  of  water  supply  as  they  are  in  other 
business.  Without  them  there  is  continual  uncertainty  with 
resulting  controversies,  and  although  it  is  not  possible  to  settle  all 
claims  by  reference  to  the  records,  yet  most  of  these  are  quickly 
adjusted  by  having  the  facts  correctly  stated.  The  principal 
records  are  those  which  show  the  amount  of  water  entering  and 
leaving  the  reservoirs  day  by  day,  the  dates,  and  quantities  taken 
into  the  canals  and  distributed  to  each  branch  or  lateral,  and  finally 
turned  to  each  wateruser.  These  records  give  by  comparison 
the  losses  by  evaporation  and  seepage,  call  attention  to  possible 
thefts  of  water,  and  form  a  guide  by  which  the  manager  from  day 
to  day  controls  the  system. 

In  addition  to  the  water  measurements,  it  is  necessary  to  have 
records  of  acreage  and  of  crops — these  being  revised  at  the  beginning 
and  end  of  each  crop  season  in  order  to  obtain  data  concerning 
the  use  of  water,  and  prevent  unlawful  diversion  from  one  field  to 
another. 

Costs. — There  are  few  reliable  figures  of  cost  of  operation  and 
maintenance,  this  being  due  largely  to  the  fact  that  there  have 
been  no  general  agreements  as  to  the  character  of  items  which 
are  to  be  included  in  this.  As  a  rule  it  may  be  said  that  the  small 
systems  operated  by  the  farmers  apparently  cost  them  from  50 
cents  to  75  cents  per  acre  per  annum,  and  sometimes  less;  but  it  is 


168      PRINCIPLES  OF  IRRIGATION  ENGINEERING 

not  possible  to  ascertain  whether  all  of  the  overhead  charges 
have  been  included  in  this,  as  much  of  the  work  is  performed  by 
volunteer  services,  and  is  not  made  a  matter  of  record.  The 
larger  systems  where  better  records  are  kept  apparently  cost 
from  $i  to  $1.50  per  acre  for  operation  and  maintenance,  not 
including  in  this  the  depreciation  or  cost  of  larger  repairs  due  to 
catastrophies. 

As  a  rule  it  may  be  stated  that  the  less  the  cost,  the  poorer  the 
results,  and  the  larger  the  losses  on  the  crop  returns.  For  every 
10  cents  per  acre  saved  in  the  apparent  cost  of  operation  and  mainte- 
nance, the  ultimate  crop  production  may  have  been  reduced  from 
$i  to  $10. 

In  examining  the  history  of  many  of  the  private  enterprises,  it  is 
extraordinary  to  see  how,  through  neglect  or  by  false  economy, 
water  has  been  kept  out  of  the  canal  during  critical  times  of  the 
year,  with  resulting  crop  losses  aggregating  tens  of  thousands  of 
dollars,  these  being  regarded  by  the  farmers  as  dispensations  of 
Providence  rather  than  as  a  result  of  their  own  ignorance  or  lack 
of  organization.  It  has  been  no  uncommon  thing  for  a  large  canal 
to  be  deprived  of  water  for  a  week  or  ten  days  during  the  extreme 
heat  of  summer,  and  the  crops  on  10,000  acres  reduced  in  value 
by  at  least  $5  per  acre — this  loss  resulting  simply  from  an  endeavor 
to  save  a  few  hundred  dollars  in  the  management. 

In  keeping  records  of  cost,  the  first  or  most  obvious  classification  is 
under  the  two  heads  of  "operation"  and  "maintenance."  It  is 
necessary  to  distinguish  somewhat  arbitrarily  between  these  as  one 
merges  into  the  other.  There  is  also  a  third  class  of  items,  which  is 
sometimes  considered,  namely,  betterments,  which  really  belongs  in 
part  in  the  original  construction  cost,  but  which  being  incurred  after 
the  canal  system  is  practically  finished,  must  be  carried  as  a  part  of 
the  maintenance  or  upkeep. 

The  operation  costs  are  usually  considered  as  including  those  items 
which  pertain  to  the  distribution  of  water  to  the  individual  farmers,  as 
distinguished  from  the  maintenance  which  relates  to  the  expenditures 
having  to  do  with  the  preservation  of  the  system. 

Each  of  these  two  classes  of  expenditure  may  further  be  divided 
into  the  principal  features  of  which  a  canal  system  consists,  namely, 
first,  storage  or  reservoir  division;  second,  the  diversion  dam  and  head- 
works;  and  third,  the  main  or  trunk  line  canal  and  principal  branches; 
fourth,  the  lateral  or  sub-lateral  system  leading  from  the  larger 
branches  to  the  individual  farms. 


OPERATION  AND  MAINTENANCE  169 

In  turn  again,  these  items  consist  of  expenditures  for  supervision, 
labor,  materials,  supplies,  etc.  Thus  carried  to  the  extreme,  the 
cost-keeping  system  should  show  the  expenditures,  for  example,  in 
labor  or  materials  in  operating  the  diversion  dam  and  headworks,  or 
in  maintaining  the  main  canal. 


CHAPTER  X 
STORAGE  WORKS 

Determination  of  Storage  Supply. — The  question  of  storage  must 
be  considered  sooner  or  later  by  the  engineers  of  any  considerable 
irrigation  system.  It  is  true  that  the  earlier  canals  taking  water  from 
perennial  streams,  and  having  first  rights  to  the  natural  flow,  may 
have  adequate  supply  for  most  of  their  lands,  but  as  the  country 
develops  even  these  canals  may  be  extended  or  enlarged.  The 
extent  to  which  this  can  be  done  depends  upon  acquiring  additional 
waters,  since  the  rights  to  water  for  new  lands  is  secondary  to  those  of 
lands  which  have  been  previously  irrigated.  Thus  it  is  that  the 
matter  of  conservation  of  the  floods,  and  of  the  waters  which  occur 
at  periods  of  the  year  when  not  needed  for  irrigation  becomes  very 
important. 

In  attempting  to  arrive  at  a  determination  of  the  storage  supply, 
there  are  several  factors  which  must  be  taken  into  account.  The  first 
question  is  relative  to  the  total  quantity  of  unappropriated  waters, 
and  the  second  has  to  deal  with  the  character  and  capacity  of  reser- 
voirs feasible  to  construct  within  reasonable  limits  of  cost.  It  is 
necessary  to  consider  also  whether  the  floods  occur  at  such  times 
and  in  such  a  manner  that  they  can  be  controlled. 

In  every  case  the  question  of  probable  cost  is  important,  and  in- 
volves taking  into  account  the  quantity  of  water  required  for  the 
lands  under  consideration;  the  latter  is  governed  largely  by  the  char- 
acter and  location  of  lands,  as  well  as  the  area  to  be  watered. 

In  practically  every  case  engineering  and  economic  questions  are 
involved,  the  former  dealing  with  the  physical  conditions  of  runoff 
and  topography,  the  latter,  with  cost  of  conserving  and  value  of  the 
supply. 

Annual  Runoff. — Of  the  engineering  questions  involved  in  storage, 
the  first  and  most  quickly  answered,  if  measurements  of  the  stream 
are  available,  is  as  to  the  annual  runoff,  or  total  quantity  of  water 
which  has  occurred  in  the  stream  each  year  in  the  recent  past.  It  is 
obvious  that  this  quantity  limits  all  future  development,  unless  the 
drainage  area  can  be  increased  by  bringing  into  it  one  or  more  streams 
from  another  basin.  The  annual  runoff  varies  largely  from  year  to 

170 


STORAGE  WORKS  171 

year,  and  in  any  one  year  may  be  several  times  that  of  a  measured 
year,  or  it  may  be  far  less. 

There  are  also  to  be  found,  in  studying  measurements  of  runoff  for 
consecutive  years,  that  in  some  one  year  there  were  practically  no 
floods,  and  that  such  a  year  may  be  preceded,  or  succeeded  by  a 
season  of  drought,  as  dry  years  frequently  occur  in  succession. 
There  are  also  to  be  expected  other  years  when  the  floods  surpass 
those  in  the  memory  of  the  oldest  inhabitant,  and  when  structures 
which  were  planned  to  meet  ordinary  conditions  may  be  swept  away. 
In  other  words,  all  proposed  works  for  storage  must  be  considered 
with  a  view  to  the  fact  that  they  must  meet  extraordinary  flood  con- 
ditions, and  may  occasionally  not  receive  much,  if  any,  water  for 
storage. 

There  have  been  in  the  past  many  efforts  to  find  some  simple  rule 
connecting  the  amount  of  rainfall  as  measured  on  the  drainage 
basin  with  the  quantity  of  water  flowing  from  it.  Some  engineers 
have  assumed  that  the  runoff  would  be  a  trifle  less  than  one-third  of 
the  rainfall.  The  attempt  to  apply  such  a  rule,  however,  under 
different  topographic  and  climatic  conditions,  has  led  to  absurd 
results,  as  in  the  arid  west,  the  runoff  may  not  exceed  2  or  3  per  cent, 
of  the  rainfall  as  measured  on  the  higher  portions  of  the  catchment 
area.  The  runoff  in  any  one  year,  especially  that  of  unusual  rainfall 
may  rise  to  10  or  12  per  cent,  over  the  entire  watershed,  or  in  a  year 
of  drought  drop  to  less  than  i  per  cent.  (For  further  discussion  see 
chapter  on  Water  Supply.) 

Amount  of  Runoff  that  can  be  Stored. — Not  all  of  the  water 
shown  by  the  measurements  of  river  flow  is  available  for  storage. 
The  records  of  river  flow  usually  show  that  a  certain  quantity  of 
water  has  passed  a  given  point  on  a  stream  during  certain  seasons  of 
preceding  years.  It  is  frequently  assumed  that  all  the  water  can  be 
held,  and  many  unwise  investments  have  been  made  because  of  the 
fact  that  extensive  works  have  been  constructed,  based  upon  the 
assumption  that  all  the  water  known  to  occur  in  the  recorded  floods 
could  be  held  in  storage  basins. 

The  limitations  upon  the  amount  of  water  which  can  be  econom- 
ically stored  are  those  arising  from  two  causes;  first,  geographical,  or 
topographical;  and  second,  hydrographic.  Under  the  first  are 
included  those  which  pertain  to  the  relative  position  on  the  drainage 
area  of  the  storage  basins.  The  best  of  these  are  usually  found 
relatively  high  up  on  the  stream  or  on  its  tributaries,  and  in  such 
positions  that  the  amount  of  flood  water  occurring  above  the  dam  site 


172      PRINCIPLES  OF  IRRIGATION  ENGINEERING 

is  relatively  small.  In  other  words,  the  greatest  floods  occur  at  points 
below  those  at  which  feasible  storage  sites  are  found.  It  may  be 
said  to  be  a  general  rule  that  the  better  the  physical  conditions  for  a 
reservoir  site,  the  less  the  amount  of  water  available  at  that  point. 
In  nature  we  frequently  find  broad  valleys  with  relatively  narrow  out- 
lets through  which  flow  insignificant  streams,  with  small,  or  irregular 
floods;  and,  on  the  other  hand  are  large  streams  with  considerable 
volume  flowing  through  narrow,  deep  valleys,  with  fall  so  great  that 
storage  reservoirs  are  out  of  the  question. 

These  hydrographic  conditions  limiting  storage  are  those  which 
arise  in  accordance  with  the  volume  and  rapidity  or  intensity  of  the 
flood  and  in  the  manner  in  which  one  flood  may  follow  another  in 
immediate  succession.  If  a  large  reservoir  is  located  on  the  main 
stream,  it  will,  of  course,  catch  all  of  the  flood  coming  into  it  up  to  the 
capacity  of  the  reservoir;  but  if,  as  is  occasionally  the  case,  the 
storage  reservoir  is  on  a  side  stream,  and  the  floods  in  the  main  stream 
must  be  diverted  by  a  flood  water  canal,  then  the  amount  of  water 
which  can  be  brought  into  such  a  reservoir  is  limited  largely  by  the 
capacity  of  this  flood  canal.  If  the  floods  occur  somewhat  slowly, 
and  do  not  exceed  the  capacity  of  this  diversion  canal,  the  maximum 
amount  can  be  stored;  but,  if  the  flood  is  flashy,  with  a  high  peak 
exceeding  the  capacity  of  the  canal,  then  a  correspondingly  less 
amount  can  be  conserved. 

It  frequently  happens  that  droughts  succeed  droughts,  and  floods 
follow  floods,  but  in  operating  reservoirs,  it  is  usually  assumed  that 
the  first  flood  will  be  caught,  and  held  to  the  full  extent.  If,  then, 
there  happens  to  be  a  second  flood  following  upon  the  first,  while  the 
reservoir  is  still  full,  and  before  it  can  be  drawn  down  for  storage 
elsewhere,  or  for  beneficial  use,  then  it  follows  that  the  second  flood 
is  largely  wasted.  Thus  it  happens  that  although  on  casual  inspec- 
tion of  the  data  of  river  flow  there  appears  to  be  a  large  volume  of 
water,  yet  careful  study  of  the  limitations  frequently  lead  to  dis- 
appointing results,  because  of  the  fact  that  only  a  small  portion  of 
the  total  amount  of  water  can  be  economically  held. 

Each  stream  or  catchment  area  must  be  studied  by  itself,  with 
reference  to  the  location  and  capacity  of  the  proposed  storage  sites, 
and  of  the  relation  of  these  to  the  particular  part  of  the  drainage 
area  tributary  to  each  storage  basin.  The  prior  appropriations,  or 
legal  claims  to  flood  water,  which  may  exist,  and  the  rapidity  of  the 
occurrence  of  floods,  must  also  be  studied  carefully  with  reference 
to  these  particular  sites.  As  a  result  it  is  frequently  necessary  to 


STORAGE  WORKS  173 

exclude  from  consideration  large  and  important  parts  of  a  drainage 
basin  because  of  the  fact  that  these  parts  are  not  tributary  to  any 
economical  reservoir  site. 

Ordinarily  it  may  be  said  that  the  building  of  a  reservoir  of 
sufficient  capacity  to  hold  all  of  the  flood  waters  from  a  given  shed 
is  impracticable,  both  from  a  physical  and  economic  viewpoint. 
It  consequently  becomes  a  question  of  determining  the  greatest 
amount  which  can  be  economically  held.  To  do  this,  it  is  sometimes 
necessary  to  consider  carefully  the  future  need  for  water  and  its 
probable  value. 

Seepage  Losses. — The  full  or  theoretical  capacity  of  any  reservoir 
is  not  always  the  amount  which  can  be  depended  upon  for  beneficial 
use.  There  are  certain  losses  which  must  be  taken  into  account, 
and  occasionally  some  gains.  The  principal  losses  are  grouped 
under  the  headings  (i)  Evaporation,  and  (2)  Seepage. 

The  evaporation  losses  are  practically  continuous  and  so  far  as 
present  knowledge  goes,  cannot  be  controlled  at  reasonable  cost. 
If  it  were  practicable  to  cover  the  reservoir  to  exclude  sunlight 
and  wind  movement,  they  could  be  reduced  to  a  minimum,  but  the 
necessary  expenditure  for  this  purpose  would  be  prohibitive.  In 
cases  where  the  spring  floods  are  held  in  a  reservoir  and  the  water 
is  drawn  down  during  the  succeeding  summer,  these  losses  are 
usually  not  very  serious.  Under  these  conditions  there  are  only 
three  or  four  months  of  evaporation  to  consider,  but  if  the  reservoir 
is  to  carry  water  over  to  years  of  drought,  then  the  total  annual 
losses  come  into  play  and  these  usually  form  a  large  proportion 
of  the  amount  stored. 

The  seepage  losses  are  frequently  matters  of  great  concern  but 
unlike  the  losses  of  evaporation  there  is  a  tendency  for  these  to 
gradually  reduce  by  the  lapse  of  time  due  to  the  silting  up  of  the 
bed  of  the  reservoir.  In  new  construction,  where  water  is  being 
held  for  the  first  time  in  basins  which  have  not  been  thoroughly 
wet  for  centuries,  the  seepage  losses  are  very  great.  Each  year 
as  the  reservoir  is  filled  higher  and  higher  and  newer  lands  are  sub- 
merged, these  losses  continue,  but  as  the  underlying  soil  becomes 
packed  through  the  presence  of  water  and  layers  of  fine  silt  are 
deposited  on  the  bottom,  there  is  a  tendency  to  render  the  under- 
lying earth  less  pervious  and  to  prevent  the  free  escape  of  the  water. 

The  accompanying  diagrams  illustrate  some  of  these  conditions 
of  losses  of  water  from  recently  built  storage  works.  They  are 
especially  instructive  as  showing  the  actual  conditions.  In  these 


174      PRINCIPLES  OF  IRRIGATION  ENGINEERING 

CLEAR  LAKE  RESERVOIR  -  CALIFORNIA  1911 


FIG.  37. — Diagram  illustrating  losses  in  reservoirs. 


STORAGE  WORKS  175 

comparison  is  made  between  several  reservoirs  of  distinctly  different 
geologic  structure;  for  example  the  East  Park  Reservoir  in  the 
Orland  project,  California,  is  in  a  basin  in  crystalline  rocks  in  the 
mountains  where  the  seepage  losses  are  probably  at  a  minimum, 
while  the  other  reservoirs  noted  are  in  a  region  of  lava  flow.  In 
the  case  of  the  East  Park  Reservoir  evaporation  may  account  for 
most  of  the  water  which  disappears.  In  comparison  with  this  is 
to  be  noted  the  Cold  Springs  Reservoir  of  the  Umatilla  project, 
Oregon,  which  is  in  a  basin  cut  in  eruptive  rocks  of  large  porosity, 
these  being  overlaid  with  somewhat  heavy  beds  of  sands,  gravel, 
and  wind-deposited  materials.  Still  larger  losses  are  shown  in 
the  Clear  Lake  Reservoir  of  the  Klamath  project,  Oregon- Cali- 
fornia. This  has  been  built  partly  for  the  purpose  of  reducing 
the  floods  in  Lost  River  and  where  the  seepage  losses  into  the  under- 
lying lava  were  anticipated  as  being  large.  Greater  losses  are 
shown  from  the  Deerflat  Reservoir  in  Boise  project,  Idaho,  where 
water  storage  is  provided  out  on  the  rolling  plains  and  where  the 
lava  is  covered  with  a  relatively  thin  layer  of  soil,  these  seepage 
losses  are  being  steadily  reduced  year  by  year  but  will  probably 
always  form  a  notable  percentage  of  the  amount  of  water  stored. 

Evaporation  Losses. — Every  body  of  water,  large  or  small, 
exposed  to  the  sun  and  wind,  is  constantly  losing  from  the  surface 
a  greater  or  less  amount,  which  is  dependent  mainly  upon  the 
temperature  and  wind  movement,  and  to  a  less  extent  upon  other 
causes — such,  for  example,  as  altitude  and  atmospheric  conditions 
as  regards  moisture.  In  the  case  of  natural  reservoirs,  spread  over 
hundreds  of  acres,  with  exposure  to  winds  which  sweep  down  the 
mountain,  and  with  a  hot  sun  pouring  from  a  cloudless  sky,  the 
losses  are  very  great,  and  become  a  notable  percentage  of  the  quan- 
tity stored.  These  losses  have  been  the  subject  of  prolonged  study 
by  various  observers — notably  those  of  the  Weather  Bureau,  and 
officials  in  charge  of  important  city  waterworks. 

As  yet  the  laws  governing  evaporation  in  large  bodies  of  water  are 
not  fully  understood,  nor  reduced  to  exact  statements.  For  the 
present  the  engineer  must  base  his  assumptions  upon  the  more  or  less 
empirical  formulae,  or  arrive  at  them  from  direct  comparison  with 
observations  of  the  rate  of  evaporation  under  similar  conditions  of 
climate  and  topography. 

The  evaporation  during  the  summer  season  with  its  higher  tempera- 
ture is,  of  course,  greater  than  during  the  winter,  although  there  is 
an  appreciable  loss  during  the  cold  weather,  even  from  the  frozen 


176     PRINCIPLES  OF  IRRIGATION  ENGINEERING 


surface  of  the  lake.  The  losses  from  the  surface  of  a  broad  shallow 
basin  are  also  greater  than  those  of  a  deep  body  of  water,  because 
of  the  higher  temperature  of  the  shallow  waters.  The  wind  movement 
also  has  a  very  important  effect,  in  that  it  carries  away  the  moisture- 
laden  air  immediately  over  the  surface,  and  permits  a  more  rapid  rate 
of  change  from  liquid  to  vapor. 

The  following  table  illustrates  the  difference  in  rate  of  evaporation 
month  by  month,  under  different  local  and  climatic  conditions.  It  is 
given  merely  as  an  illustration,  and  as  demonstrating  that  the  loss 
by  evaporation  is  large: 

DEPTH  OF  EVAPORATION  IN  INCHES,  BY  MONTHS 


Month 

Neb. 

Idaho 

Oregon 

Lake 
Tahoe 

Nevada 

Wash. 

N.  Mex. 

Arizona 

Jan. 

i  -z 

I     «CO 

O    CO 

I.  75 

i  .  71; 

I    7<? 

2     <O 

4    ^0 

Feb  
Mar  

i-75 
3  .  oo 

2.25 
4.  oo 

1-25 
3  •  27 

i-75 

I  .  7C 

i-75 

2.  2<J 

2.50 
6.25 

2.75 

4.  ^o 

4-75 
6.25 

Apr.  . 

4    CO 

7    2< 

6  64 

2    OO 

3  2^ 

7   01 

8  oo 

o  oo 

May 

6    2< 

10  68 

7    I  £ 

3    CO 

r    2< 

8  36 

II     <O 

II     ?O 

June  . 

8.  ex 

II  .  OC, 

6.  oo 

c.  .00 

7.86 

8.00 

13    4"> 

13    50 

July  
AUK..  . 

io-95 
9.  39 

11.15 
11.77 

8.01 

Q.  21 

6.49 

7.42 

9.86 
8.70 

10.74 
9  -41 

u-57 
10.48 

14.25 

14.  23 

Sent 

7   44 

Q     7C 

6.13 

7.  7<J 

e    j7 

e    ei 

8  58 

13  .  76 

Oct 

r    en 

r    4.0 

2     <?O 

4    33 

3    3S 

3    It 

6  76 

II    31 

Nov  

4.  oo 

2  .  70 

I.OO 

3.13 

2  .  C.O 

2  .OO 

3-86 

7.  7Q 

Dec  

3.00 

1-50 

0.50 

2.25 

2.OO 

2.OO 

3-oo 

4.65 

Totals  

65.67 

79.60 

53-45 

42.21 

53-65 

67.96 

86.95 

115.18 

The  above  figures  of  depth  of  evaporation  are  probably  the  results 
of  observation  by  Professor  Frank  Bigelow  of  the  U.  S.  Weather 
Bureau  (Engineering  News,  Vol.  63,  p.  694,  June  16,  1910).  Many 
of  the  figures  are  interpolations,  but  they  represent  the  results  of  ob- 
servations of  evaporation — not  from  reservoirs,  but  from  pans, 
usually  4  ft.  in  diameter,  located  on  the  ground.  The  losses  from  a 
large  body  of  water  may  be  more,  but  presumably  are  less.  Ob- 
servations indicate  that  there  is  a  nearly  uniform  rate  of  evaporation 
over  the  area  of  the  water  surface  of  a  lake  or  pond,  beginning  at  a 
short  distance  from  the  shore. 

It  should  be  kept  clearly  in  mind  that  these  figures,  and  similar 
figures  frequently  quoted,  represent  the  losses  from  relatively  small 


STORAGE  WORKS  177 

areas,  and  not  from  the  lake  surface  itself.  There  is  a  very  great 
difference  in  the  amount  of  evaporation  from  pans  placed  side  by 
side,  depending  upon  their  diameter  and  height  of  rim  of  the  pan 
above  the  surface  of  the  water;  and  there  is  no  known  relation  between 
the  evaporation  from  a  pan  of  a  given  size  and  an  open  body  of  water ; 
the  losses  in  each  case  may  be  greater  or  less,  dependent  upon  many 
conditions. 

In  looking  over  these  figures,  it  is  to  be  noted  that  although  the 
total  evaporation  for  the  year  may  be  approximately  the  same  for 
different  localities,  the  distribution  of  this  by  months  is  variable, 
dependent  upon  climatic  conditions  prevailing  at  the  time.  For 
example,  in  Oregon  observations  of  winter  evaporations  show  a 
remarkably  low  loss  as  compared  with  the  others.  All  show  a  maxi- 
mum in  July  or  August,  the  rate  of  evaporation  dropping  off  rapidly 
after  these  months. 

The  effect  of  evaporation  in  reducing  available  storage  capacity 
will  depend  upon  the  size  and  depth  of  the  reservoir,  and  also  the 
length  of  time  that  water  must  be  held  in  storage;  that  is  to  say,  the 
percentage  of  loss  from  a  large,  shallow  reservoir  is  far  greater  than 
from  a  small  but  deep  one  of  equal  capacity;  also,  the  relative  loss 
from  a  storage  supply  held  during  a  single  irrigation  season  will  be 
far  less  than  if  water  must  be  held  over  from  one  year  to  the  next. 

The  losses  by  evaporation  of  6  in.  in  depth  during  a  month  of 
thirty  days,  on  a  reservoir  having  a  surface  area  of  3,000  acres  is 
equivalent  to  a  steady  flow  throughout  the  thirty  days,  of  approxi- 
mately 25  second-feet. 

Ratio  of  Runoff  to  the  Storage  Capacity. — The  relation  which 
the  total  runoff  or  amount  of  water  delivered  from  a  given  drainage 
basin  bears  to  the  storage  possibilities  is  one  of  the  first  objects  of 
concern  to  the  engineer  interested  in  the  conservation  and  develop- 
ment of  a  water  supply.  As  a  rule  it  may  be  stated  that  the  larger 
the  runoff  per  square  mile  drained,  the  less  the  probabilities  of 
finding  good  storage  sites.  This  is  because  of  the  fact  that  with 
large  runoff  the  streams  through  past  ages  have  eroded  their  channels 
and  have  carved  broad  outlets  through  various  obstructions,  making 
it  difficult  to  create  artificial  basins.  On  the  other  hand,  with 
reduced  runoff  per  square  mile,  the  streams  have  become  over- 
loaded with  sand  and  gravel;  their  beds  are  now  choked  and  they 
have  not  been  able  to  cut  such  outlets  in  the  natural  barriers.  This 
general  rule  is,  of  course,  modified  by  geologic  conditions,  especially 
where  ancient  glaciers  have  built  morains  across  the  valleys,  or 
12 


178      PRINCIPLES  OF  IRRIGATION  ENGINEERING 

where  there  has  been  the  tilting  of  the  earth's  crust  in  one  direction 
or  another,  changing  the  former  slopes  and  bringing  in  new 
complications. 

The  amount  of  total  runoff  is  a  quantity  which  cannot  be  modified 
appreciably  by  man.  It  varies  from  year  to  year  according  to  the 
climatic  oscillations.  The  portion  of  this  which  may  be  put  to 
beneficial  use  is,  however,  dependent  quite  largely  upon  human 
agencies.  It  is  assumed  to  be  practicable  to  begin  systematic 
forest  protection  at  the  head-waters,  and  thus  exercise  a  beneficial 
influence  upon  the  way  in  which  the  runoff  conies  from  the  steep 
slopes.  It  is  now  generally  believed  to  be  essential  to  the  full 
conservation  of  the  water  supply  that  the  catchment  areas  of  the 
streams  be  studied  and  controlled  with  reference  to  the  covering 
of  trees,  shrubs,  grass,  etc.  Assuming  that  this  is  done,  and  that 
the  violence  of  extreme  floods,  or  the  rapidity  of  runoff  is  modified 
as  far  as  practicable  by  good  forest  and  grazing  conditions,  then  the 
question  next  in  order  is  that  of  proportion  of  the  water  flowing 
in  the  stream  which  can  be  controlled. 

On  most  streams  within  the  irrigated  region,  the  ordinary  summer 
flow  has  already  been  appropriated  and  put  to  beneficial  use.  Canals 
have  been  built  with  capacity  sufficient  to  take  all  of  the  normal 
flow  during  the  crop  season.  Assuming  that  this  is  the  case,  the 
next  question  is  with  reference  to  the  waters  which  occur  in  the 
stream  at  times  other  than  during  the  crop  season,  and  also  of  the 
floods  which  take  place  in  the  spring  or  early  summer,  and  which 
exceed  in  volume  the  capacity  of  the  canals  already  built. 

All  of  the  water  which  flows  before  and  after  the  crop  season, 
or  at  the  times  when  not  actually  needed  for  irrigation  during  the 
season,  should  be  held  for  use  later,  and  under  ordinary  conditions 
it  may  be  considered  as  available  for  storage.  However,  there 
has  recently  grown  up  a  practice  which  has  resulted  in  some  doubts 
and  legal  controversies.  Some  of  the  oldest  appropriators  are 
attempting  to  use  the  fall  and  winter  waters  for  flooding  the  farming 
lands  after  the  crops  are  removed,  with  the  idea  of  saturating  these 
lands  as  far  as  possible,  in  order  to  reduce  the  amount  of  water 
needed  during  the  succeeding  crop  season.  There  are  a  few  con- 
ditions of  soil  and  climate  where  this  can  be  done  effectively,  but 
there  is  always  a  question  as  to  whether  this  is  not  a  wasteful  use 
of  water.  In  the  case  of  heavy,  or  loose  gravels  underlying  the 
soil,  it  appears  probable  that  even  though  these  gravels  are  filled 
with  water  during  the  fall  and  winter,  yet  before  spring  they  will 


STORAGE  WORKS  179 

drain  out  and  the  benefits  derived  will  not  be  comparable  with  the 
resulting  waste.  Because  of  this  condition,  conflicts  have  arisen 
between  the  reservoir  men  on  the  one  hand  claiming  that  they  are 
entitled  to  this  water  out  of  the  crop  season,  and  the  farmers  on  the 
other,  who  claim  that  they  are  entitled  under  their  appropriations 
to  all  the  water  they  desire  to  use  throughout  the  year,  and  that  they 
should  be  permitted  to  store  it  in  the  ground  in  the  manner  described. 

Regarding  the  floods,  there  has  been  no  serious  question  as  to 
the  fact  that  the  portion  of  these  in  excess  of  the  capacity  of  the 
irrigating  canals  should  be  stored.  These  floods  usually  occur 
at  the  beginning  of  the  crop  season,  and  hence  the  length  of  time 
during  which  they  are  stored  and  the  consequent  losses  by  evapora- 
tion, are  at  the  minimum. 

Determination  of  Storage  Required. — Having  ascertained  the 
limitation  of  the  possible  storage  set  by  physical  conditions,  such  as 
quantity  of  water,  and  capacity  of  feasible  storage  basins,  the  suc- 
ceeding questions  are  generally  easily  answered,  because  it  is  usually 
assumed  that  the  entire  available  quantity,  extreme  flood  excepted, 
will  be  held  for  future  use.  It  occasionally  happens,  however,  that 
the  area  of  irrigable  land  which  can  be  reached  from  any  one  storage 
reservoir,  or  system  of  reservoirs  is  limited,  and  in  that  case  the 
question  is  narrowed  to  the  actual  needs  of  this  particular  tract  of 
land.  It  is,  of  course,  not  economical  to  go  to  the  extreme  of  pro- 
viding more  storage  than  is  actually  needed,  and  on  the  other  hand  the 
possible  crop  losses  will  not  justify  providing  inadequate  storage. 

Theoretically,  the  storage  reservoir  should  be  of  such  capacity  that 
it  can  be  drawn  upon  whenever  needed  to  supplement  the  ordinary 
supply  received  from  the  unregulated  flow  of  the  stream.  Nearly 
every  irrigable  tract  is  enabled  to  obtain  water  from  a  perennial  or 
intermittent  stream,  flowing  during  the  early  part  of  the  crop  sea- 
son and  the  storage  reservoir  is  intended  to  supplement  this  sup- 
ply. In  some  cases,  however,  this  is  so  irregular  that  the  storage 
reservoir  must  be  large  enough  to  take  care  of  the  entire  tract. 

The  first  question,  therefore,  is:  What  dependence,  if  any,  should 
be  placed  upon  the  natural  flow?  This  varies  greatly  from  year  to 
year,  and  in  any  period  of  ten  or  twenty  years  there  is  some  one  year 
which  is  much  lower  than  all  the  rest.  Under  the  existing  crop  con- 
ditions, is  it  economical  to  make  provision  to  take  care  of  this 
exceptionally  low  year,  or  will  the  expense  of  so  doing  not  justify  the 
results?  In  other  words,  is  it  not  better  to  figure  on  reduced  crop 
production  during  this  one  year  than  to  make  extraordinary  provision 


180      PRINCIPLES  OF  IRRIGATION  ENGINEERING 

for  it?  In  such  case,  knowing  in  advance  that  there  may  not  be 
enough  water,  the  farmers  are  warned  to  economize  the  water  in 
saving  the  trees,  and  to  take  their  risks  upon  the  least  valuable  of 
the  annual  crops.  This  question  of  economical  importance  of  crop 
failure  one  or  more  years  in  every  ten  must  be  balanced  against  the 
probable  cost  and  practicability  of  providing  against  the  exceptional 
year. 

Having  made  certain  assumptions  as  to  the  requirements  of  mini- 
mum years,  there  then  follows  the  assumption  as  to  the  amount  of 
water  which  can  be  depended  upon  by  natural  flow,  if  any,  during 
these  years,  and  the  amount  which  must  be  stored  to  provide  the 
supplemental  supply.  The  assumptions  of  minimum  year  require- 
ments will,  of  course,  vary  under  different  conditions  of  climate  and 
character  of  crops  to  be  raised.  Under  certain  conditions,  it  may  be 
assumed  that  for  one  year  in  ten,  or  twenty,  it  will  not  be  econom- 
ically possible  to  provide  a  complete  supply.  This  may  be  justified 
by  the  fact  that  the  losses  during  that  one  year  will  be  more  than 
balanced  by  the  saving  in  the  cost  of  storage  works. 

This  minimum  flow  does  not  occur  throughout  the  crop  season,  but 
for  certain  months,  or  portions  of  months;  and  for  the  other  months 
it  is  not  necessary  to  provide  the  same  amount  of  storage.  That  is 
to  say,  from  day  to  day  there  will  be  a  greater  or  less  quantity  of 
water  available  from  the  stream,  and  there  will  be  a  greater  or  less 
demand  for  this,  according  to  the  needs  of  the  crops.  The  difference 
between  the  probable  amount  which  can  be  had  from  the  stream, 
and  the  probable  regular  demands  from  the  farmers,  measures  the 
quantity  which  should  be  available  in  the  reservoir. 

The  sum  total,  however,  of  these  daily  demands  upon  the  reser- 
voir do  not  by  any  means  measure  the  storage  required.  This  must 
be  increased  to  meet  losses: 

(a)  by  evaporation  which  is  dependent  upon  length  of  time 
stored  and  climatic  conditions; 

(b)  seepage  in  the  reservoir  itself; 

(c)  losses  of  water  in  transit  from  the  reservoir  to  the  lands; 

(d)  other  losses,  often  unaccountable,  mainly  due  to  improper 
methods  of  handling  and  distribution. 

The  storage  capacity  also  is  modified  by  the  fact  that  there  is  more 
or  less  accumulation  in  the  reservoir  due  to  irregular  storms,  at  the 
same  time  that  these  losses  are  occurring,  so  that  we  have  a  constantly 
fluctuating  burden  to  be  carried  by  the  reservoir. 


STORAGE  WORKS  181 

The  amount  of  storage  required,  as  is  obvious  from  the  preceding 
statements  is  not  a  simple  matter  directly  comparable  with  the  acre- 
age to  be  served;  first,  because  this  acreage  may  be  supplied  in  part  by 
a  fluctuating  flow  of  the  stream;  and,  second,  because  its  require- 
ments for  water  vary  from  day  to  day.  As  far  as  practicable,  a 
schedule  should  be  made  in  advance  of  the  probable  needs  of  the  land, 
depending  upon  the  character  of  crop,  and  the  time  of  year  when  the 
various  crops  require  certain  amounts  of  water.  If  most  of  the 
fields  are  in  alfalfa,  this  will  require  water  at  intervals  of  two  or  three 
weeks  throughout  the  entire  growing  season,  or  even  late  in  the  fall; 
whereas,  if  more  of  the  land  is  in  wheat  or  smaller  grain,  and  this  is 
not  followed  by  another  crop,  the  irrigation  may  be  finished  early  in 
the  summer,  and  largely  by  waters  taken  directly  from  the  river. 

In  considering  the  question  of  storage,  therefore,  it  is  necessary  to 
assume  what  are,  or  will  be,  the  principal  crops  of  a  region,  and  the 
time  of  year  when  these  will  probably  be  irrigated.  In  other  words, 
make  certain  assumptions  as  to  the  total  amount  of  water  which 
should  be  delivered  day  by  day.  From  this  is  to  be  deducted  the 
probable  amount  which  may  be  obtained  without  regulation  from 
the  natural  flow  of  the  stream,  including  floods.  The  difference  rep- 
resents the  deficiency  which  should  be  supplied  by  storage  on  the 
given  days  or  periods  of  time,  and  a  study  of  these  probable  daily 
demands  will  show  that  the  reservoir  need  not  be  planned  with  ref- 
erence to  the  entire  amount  of  water  which  will  be  used  during  the 
year,  but  rather  with  reference  to  a  fluctuating  quantity.  The 
problem  thus  is  not  one  of  simply  ascertaining  the  details  for  the  year 
of  river  flow,  and  of  water  to  be  applied  to  the  land;  but,  on  the  con- 
trary, that  of  an  analysis,  day  by  day,  of  the  varying  quantities — 
each  modified  by  climatic  conditions  as  regards  supply  and  probable 
crop  conditions,  as  regards  needs  of  water. 

Economic  Questions  in  Storage. — Water  storage  for  irrigation  is 
relatively  a  new  subject  as  regards  the  economic  considerations. 
Irrigation  itself  is  as  old  as  civilization,  and  the  questions  of  canal 
construction  and  the  diversion  of  the  water  to  the  land  by  gravity 
are  fairly  well  understood.  Water  storage  for  agriculture  also  has 
been  practised  to  a  certain  extent,  especially  in  India,  but  there  has 
not  yet  been  developed  a  consistent  theory,  or  set  of  rules,  based 
upon  economic  considerations.  Each  case  of  storage  has  been  con- 
sidered by  itself  with  reference  to  local  conditions,  probable  amount 
of  money  available  for  expenditure,  the  works  being  built  accordingly 
and  then  modified  on  the  basis  of  further  experience. 


182      PRINCIPLES  OF  IRRIGATION  ENGINEERING 

Theoretically,  water  conservation  by  storage  should  be  extended 
to  a  full  limit  of  the  amount  of  water  which  occurs  in  nature.  As  a 
rule  there  is  more  good  land  needing  water  than  there  is  water  to 
supply  it;  and  wherever  this  holds  true,  it  would  seem  to  follow  that 
every  drop  of  water  should  be  held  to  irrigate  the  lands.  There 
comes  in  here,  however,  the  question  of  cost.  To  take  an  extreme 
case,  there  will  be  in  a  given  period  of  twenty  years  one  excessive 
flood.  The  waters  of  this  flood  cannot  be  held  indefinitely  in  a  basin, 
because  they  will  escape  by  evaporation.  Even  if  any  considerable 
part  could  be  held,  the  question  arises  as  to  whether  the  cost  of  pro- 
viding a  large  enough  basin  would  be  justified  by  the  value  of  the 
waters,  coming,  say  once  in  twenty  years.  The  agricultural  develop- 
ment of  the  country  could  not  be  economically  adjusted  to  utilize 
this  irregular  supply,  especially  as  the  time  of  occurrence  could  not  be 
known  in  advance.  In  short,  by  considering  an  extreme  case,  it  is 
recognized  that  there  are  few  conditions  where  all  of  the  flood  waters 
can  be  economically  held.  We  must,  therefore,  figure  on  holding  less 
than  the  total  flow,  especially  in  the  extremely  wet  years. 

Coming  down  the  scale  from  the  excessive  floods,  we  finally  reach 
a  place  where  it  becomes  an  evenly  balanced  matter  of  cost  and 
benefits;  that  is  to  say,  the  floods  which  occur  every  year,  or  four 
years  out  of  five,  should  undoubtedly  be  saved,  if  possible,  because 
for  the  fifth,  or  dry  year,  some  water  may  be  held  over,  or  the  area  of 
annual  crops  can  be  reduced.  Starting  from  the  other  extreme,  it 
may  be  also  said  that  storage  should  not  be  neglected,  because  there 
are  known  to  occur  certain  years,  once  in  ten  or  twenty,  when  there 
are  practically  no  floods.  It  would  be  unwise  to  assume  that  because 
such  a  year  occasionally  occurs,  therefore,  no  storage  should  be 
provided. 

We  thus  have  an  intermediate  point  somewhere  between  these 
two  extremes — namely,  that  storage  in  general  should  not  be  con- 
sidered for  extreme  floods;  nor  should  it  be  limited  to  the  minimum 
flood. 

A  determination  of  this  intermediate  point  rests  upon  crop  values 
immediate  or  prospective.  If  the  climate  is  cold  and  the  principal 
crops  are  such  as  to  bring  but  low  returns  per  acre,  then  there  is 
little  justification  in  making  a  large  expenditure  for  the  storage, 
such  as  would  be  practicable  and  desirable  in  warmer  climates, 
where  crop  follows  crop  in  rapid  succession  and  where  the  unit 
value  per  acre  of  crops  is  large. 

The  immediate,  or  present  value  of  the  crops  produced  in  an  area 


STORAGE  WORKS  183 

should  not  be  used  as  the  limiting  feature,  because  it  is  proper  to 
assume  that  with  more  complete  development  of  the  area,  there  will 
result  larger  crop  production,  and  better  facilities  for  marketing 
and  handling  this.  It  is  also  safe  to  assume  that  ordinarily  when 
the  country  is  developed,  there  can  be  no  over-production  in  the 
sense  that  such  large  quantities  of  crops  will  be  produced  that  thfe 
value  will  decrease.  This  condition  may  exist  temporarily,  but 
with  irrigated  lands  forming  such  a  small  percentage  of  the  arid 
west,  this  condition  cannot  be  permanent;  hence,  it  is  desirable 
to  use  a  reasonable  optimism  with  regard  to  future  crop  values, 
basing  these  not  upon  the  temporary  conditions  of  extremely  high  or 
low  values,  but  upon  those  which  may  be  considered  more  nearly 
normal. 

Cost  of  Storage. — From  what  has  been  stated  before,  it  is  apparent 
that  in  this,  as  in  other  operations,  the  determining  factor  in  water 
storage  is  cost;  both  absolute,  as  dependent  upon  the  amount  of 
money  available,  and  relative,  as  regards  the  benefits  which  may 
be  derived.  To  illustrate  this  point,  we  may  consider  two  extreme 
cases:  If  the  area  under  consideration  is  capable  of  high  develop- 
ment, or  is  practically  suburban  in  character,  with  genial  climate, 
such  as  that  of  the  State  of  California,  the  conditions  approach 
those  of  water  storage  for  a  city  where  almost  any  amount  of  money 
can  be  expended,  the  cost  of  storage  of  $100  per  acre-foot  may  not 
be  beyond  consideration. 

On  the  other  extreme,  where  the  lands  to  be  supplied  are  mainly 
used  for  forage  crops,  the  cost  of  storage  of  $5  per  acre-foot  may  give 
rise  to  hesitation.  Between  these  two  there  is  a  wide  range  of 
amounts  which  may  be  considered.  The  following  table  gives 
some  costs  which  have  actually  been  incurred.  In  arriving  at  these 
the  total  capacity  of  the  reservoir  is  taken,  irrespective  of  the  fact 
as  to  whether  this  is  filled  each  year,  or  whether  it  is  increased  by 
serving  as  a  temporary  or  regulating  reservoir,  as  for  the  present 
purposes,  it  is  assumed  that  each  reservoir  has  been  built  to  its 
maximum  feasible  capacity. 


184      PRINCIPLES  OF  IRRIGATION  ENGINEERING 


COST   OF   RESERVOIRS   COMPLETED   BY   UNITED   STATES   RECLAMATION 
SERVICE,  DECEMBER  31,  1911 


State 

Name  of 
reservoir 

Available1 
capacity 

Cost  to  December  31, 
1911 

Total 

Per  acre- 
foot 

Arizona 

Roosevelt  
Clear  Lake  . 

1,284,000 
462,000 
45,600 
173,000 
150,000 
40,000 
50,000 
203,770 
13,000 
34,000 
1,025,000 
456,000 
380,000 

$3,746,696.41 
127,408.61 
264,929.66 
904,542.68 
569,278.86 
154,019.19 
442,786.10 
1,242,438.77 
328,169.  26 
429,121.13 

i>739>675  -81 
1,191,734.21 
441,023.04 

$2.92 
.28 
5-82 
5.22 
3.80 
3-86 
3-84 

6.12 

2.52 
12.60 
1.70 
2.62 
1.16 

California 

California          

East  Park  

Idaho 

Deer  Flat  
Lake  Walcott 

Idaho 

New  Mexico 

Hondo  
Cold  Springs  
Belle  Fourche  

Oregon  

S.  Dakota 

Washington 

Conconully  
Bumping  Lake 

Washington  
Wyoming  
Wyoming  

Pathfinder  
Shoshone  
Snake  R.  Storage.  .  . 

Wyoming 

Grand  totals 

4,316,370 

$11,582,649.21 

Average 
2  70 

1  Acre-feet. 


CHAPTER  XI 
RESERVOIR  SITES 

General  Requirements. — A  good  reservoir  site,  from  a  purely 
topographic  standpoint,  may  be  considered  as  one  where  a  broad 
valley  or  expansion  may  be  permanently  closed  by  a  dam  of  reason- 
able dimensions.  In  order,  however,  that  such  a  site  may  have 
value  for  storage  purposes,  a  water  supply  is  also  necessary.  In 
his  search  for  a  reservoir  site  the  engineer  must,  therefore,  confine 
his  attention  to  the  valleys  of  streams  of  undoubted  water  supply, 
or  to  near-by  valleys  into  which  such  streams  may  be  diverted. 

The  capacity  of  a  reservoir  which  may  be  formed  at  a  given  site, 
compared  with  the  mean  annual  runoff  at  that  point,  is  also  a 
matter  of  some  importance.  It  is  obvious  that  to  construct  a 
reservoir  so  large  that  it  would  be  filled  but  once  in  twenty  years, 
or  possibly  not  at  all,  would  involve  a  useless  expenditure.  On 
the  other  hand,  a  reservoir  so  small  that  it  would  hold  only  a  portion 
of  each  year's  runoff  would,  in  general,  cost  more  per  unit  of  capacity 
than  one  of  larger  size. 

The  ideal  reservoir  site  is  one  which  can  be  economically  con- 
structed to  a  capacity  sufficient  to  hold  all  of  the  runoff  from  its 
tributary  watershed,  except  that  from  extraordinary  floods  which 
may  come  once  in  ten  or  twenty  years,  or  possibly  at  less  frequent 
intervals. 

It  may  sometimes  occur  that  the  amount  of  storage  capacity 
required  is  limited  by  the  area  of  irrigable  land  in  the  immediate 
vicinity.  What  is  wanted  in  this  particular  case  is  not  the  most 
economical  storage  for  the  entire  stream's  supply,  but  the  most 
economic  for  the  capacity  required.  In  such  cases  there  are  fre- 
quently a  number  of  sites  from  which  to  choose.  Even  in  such 
cases  consideration  should  be  given  to  possible  future  developments, 
and  other  things  being  equal,  or  nearly  so,  preference  given  to  the 
reservoir  site  whose  capacity  may  be  increased  to  meet  possible 
future  needs. 

Good  reservoir  sites  like  good  gold  mines  are  scarce,  and  as  in 
the  case  of  gold  mines  there  are  almost  innumerable  prospects  which 
are  popularly  supposed  to  be  valuable  but  which,  upon  further 

185 


186      PRINCIPLES  OF  IRRIGATION  ENGINEERING 

examination,  prove  to  have  some  fundamental  defect.  In  beginning 
a  reconnaissance  of  any  area,  the  inhabitants  of  that  region  will 
call  attention  to  the  innumerable  localities  where  in  their  opinion 
water  might  be  held,  but  at  a  glance  an  experienced  engineer  will 
see  that  usually  the  capacity  of  the  basin  is  too  small  to  justify 
the  cost  of  a  dam  because  the  floor  of  the  valley  is  usually  found 
to  slope  at  such  a  high  angle  that  little,  if  any,  water  could  be  held 
behind  a  dam  of  moderate  height.  To  the  uneducated  eye  the 
valley  may  appear  to  be  level. 

Survey  of  Reservoir  Sites. — Before  entering  upon  definite  surveys 
it  is  necessary  that  a  reconnaissance  be  made  of  the  entire  lower 
portion  of  the  area  or  watershed  of  the  stream  to  ascertain  roughly 
the  relative  value  of  the  various  possibilities.  For  the  purpose  of 
this  reconnaissance  the  very  best  field  man  of  largest  experience 
is  none  too  good.  It  is  his  duty  to  weigh  carefully  the  apparent 
advantages  and  disadvantages  of  each  locality  and  then  recommend 
definite  surveys.  As  all  such  surveys  involve  the  employment 
of  a  considerable  number  of  men  and  are  quite  expensive,  it  is 
incumbent  upon  the  man  making  the  reconnaissance  to  judge 
accurately  and  thus  avoid  as  far  as  possible  useless  surveys  or 
examinations  involving  merely  negative  results. 

After  it  has  been  found  by  careful  reconnaissance  that  the  choice 
of  the  reservoir  sites  is  narrowed  to  a  relatively  few  places,  then 
arrangements  should  be  perfected  for  a  careful  topographic  survey 
resulting  in  a  contour  map  of  the  storage  basin.  This  map  should 
ordinarily  be  made  with  sufficient  accuracy  to  determine  the  capacity 
of  the  basin  to  within  5  per  cent.  Greater  accuracy  than  this  is 
generally  not  necessary  but  in  some  cases  is  desirable. 

The  map  of  the  reservoir  site  should  be  made  on  a  scale  of  from 
1,000  ft.  to  2,000  ft.  to  the  inch,  dependent  upon  the  size  of  the 
basin  and  nature  of  the  topography,  the  scale  being  chosen  so  as  to 
afford  reasonable  accuracy  for  each  particular  case.  At  the  site 
of  the  dam,  however,  where  excavation  is  to  be  undertaken  and  where 
large  expenditures  are  made,  it  is  necessary  to  have  a  far  more 
elaborate  map  than  for  the  rest  of  the  reservoir.  Here  a  scale  of 
from  100  ft.  to  400  ft.  to  the  inch  is  desirable.  In  Fig.  38  is  given 
a  portion  of  such  a  map  with  contour  interval  of  5  ft.  and  the  final 
location  of  the  dam  with  related  works  sketched  upon  it. 

These  surveys  may  be  made  most  quickly  and  economically 
by  means  of  the  plane-table,  if  the  engineer  in  charge  is  accustomed 
to  the  use  of  that  instrument  and  can  sketch  accurately  and  rapidly. 


RESERVOIR  SITES 


187 


If  a  plane-table  man  and  necessary  instruments  are  not  readily 
obtainable,  the  survey  can  be  made  by  the  slower  and  more  expensive 
way  of  running  out  contours  or  marking  cross-sections  and  locating 
these  by  transit  and  level  and  then  sketching  in  the  contours  from 
these  somewhat  accurately  determined  points. 


FIG.  38. — Portion  of  topographic  map  of  dam  site  with  related  works  sketched 
upon  it.     Strawberry  Valley  Project,  Utah. 

Contour  Maps. — The  contour  maps  which  result  from  the  various 
methods  of  survey  should  be  drawn  on  a  scale  as  above  indicated 
and  should  show  sufficient  detail  to  enable  a  thorough  study  in 
the  office  of  the  essential  features/  For  this  purpose  the  contour 
interval  of  the  reservoir  basin  unless  this  is  very  large,  should  be 
5  ft.  and  of  the  dam  site  should  be  i  or  2  ft.  All  rock  outcrops, 
especially  near  the  dam  site,  should  be  indicated  and  all  cultural 
features  such  as  roads,  buildings  and  fences  clearly  shown,  together 
with  the  character  of  vegetation  and  of  soil.  Information  of  this 
kind  is  needed,  not  only  in  connection  with  the  engineering  features, 
but  in  adjusting  claims  for  damages,  rights-of-way  or  interference 
with  public  travel.  In  fact  there  is  hardly  any  detail  which  can  be 
shown  on  the  map  but  which  may  be  needed  in  determining  the 


188      PRINCIPLES  OF  IRRIGATION  ENGINEERING 

value  of  the  reservoir  and  in  making  plans  for  constructing  and 
operating  it. 

Computation  of  Capacities. — The  capacities  of  a  reservoir  site 
at  various  elevations  of  water  surface  are  determined  from  the 
contour  maps.  As  a  rule  the  area  enclosed  by  each  contour  is 
measured  by  a  planimeter,  the  results  being  determined  in  acres. 
The  mean  of  the  area  in  acres  between  any  two  contours  multiplied 
by  the  vertical  distance  in  feet  between  the  contours  gives  approxi- 
mately the  capacity  in  acre-feet.  The  mathematical  inaccuracy 
of  this  method  is  no  greater  than  that  involved  in  ascertaining  the 
exact  area  of  the  water  surface  at  the  different  elevations. 

In  cases  where  accurate  contours  have  not  been  drawn  but  cross- 
sections  run  at  short  intervals  the  capacity  may  be  determined  by 
taking  the  mean  area  of  any  two  sections  and  multiplying  this  by  the 
distance  between  them,  the  sum  of  the  various  elements  thus  deter- 
mined being  the  total  capacity.  Results  obtained  by  this  method 
are  usually  in  cubic  feet  which  may  be  reduced  to  acre-feet  by 
dividing  by  43,560. 

At  the  bottom  of  the  reservoir  is  frequently  a  dead  space,  that  is, 
water  below  a  certain  elevation  dependent  upon  the  location  of  the 
lowest  workable  gates,  is  seldom  if  ever  drawn  upon.  This  dead 
space  is  in  time  filled  with  sediment  if  the  water  is  muddy.  A 
deduction  should  be  made  from  the  theoretical  capacity  of  the  reser- 
voir, allowing  for  this  unavailable  capacity. 

Choice  of  a  Reservoir  Site. — It  occasionally  happens  that  there  is 
opportunity  for  choice  between  different  possible  sites.  As  a  rule, 
however,  good  reservoir  sites  are  so  rare  that  there  is  only  one  that 
is  worthy  of  consideration,  but  occasionally  the  choice  must  lie  be- 
tween those  which  offer  the  fewest  objections.  In  making  choice, 
therefore,  it  is  a  question  of  balancing  these  objections  rather  than  of 
considering  the  benefits.  The  first  and  usually  the  determining 
factor  is  that  of  the  cost  per  acfe-foot,  this  cost  being  not  far  from 
$5  in  the  case  of  the  ordinary  successful  irrigation  reservoir.  Next 
to  the  first  cost  is  that  of  maintenance  and  depreciation,  which  in 
turn  is  determined  by  the  probable  life  of  the  reservoir.  As  a  rule 
the  maintenance  cost  is  very  low  excepting  in  case  of  earthen  dams, 
where  continual  vigilance  must  be  exercised  and  frequent  small 
repairs  to  prevent  defects  developing. 

The  question  of  life  of  the  reservoir  or  annual  depreciation  due  to 
its  gradual  filling  up  with  material  washed  from  the  sides  is  of  great 
importance.  A  dam  constructed  in  the  course  of  main-drainage 


RESERVOIR  SITES  189 

channel  which  receives  all  of  the  storm  waters  with  accumulated 
gravels,  sand,  mud  and  debris,  must  hold  behind  it  practically  all  of 
this  solid  matter.  The  clearer  waters  may  be  drawn  down  but  in 
time  this  solid  matter  will  accumulate,  and  in  the  course  of  decades 
reduce  the  capacity  of  the  reservoir.  On  the  other  hand,  if  a  similar 
dam  is  built  on  a  side  channel  which  does  not  habitually  receive  the 
waters  from  the  great  storms  the  reservoir  may  be  filled  by  a  large 
flood  canal  from  the  main  stream  and  this  flood  canal  may  be  manipu- 
lated in  such  a  way  as  to  receive  the  principal  parts  of  the  flood  waters 
while  rejecting  and  washing  back  into  the  main  drainage  all  of  the 
gravel  and  sand,  and  most  of  the  mud. 

Shallow  and  Deep  Reservoirs. — There  is  sometimes  opportunity 
for  choice  between  two  possible  reservoir  sites  based  upon  the  rela- 
tive surface  exposure  as  compared  with  the  depth  of  water.  The 
shallower  one  will  first  lose  more  water  by  evaporation  because  of 
the  greater  rapidity  with  which  the  water  is  heated  by  the  sun, 
and  second  because  of  the  larger  area  from  which  evaporation  is 
taking  place.  Counterbalancing  this,  however,  is  the  fact  that  the 
shallow  reservoir  is  usually  cheaper  to  construct,  as  it  involves  gen- 
erally the  building  of  a  dam  of  less  height. 

Where  the  water  supply  is  limited  and  must  be  conserved  to  the 
highest  degree  the  deep  reservoir  possesses  decided  advantages 
over  the  shallow  one  on  account  of  the  smaller  losses  by  evaporation. 
Especially  is  this  true  if  the  storage  supply  must  be  carried  over  from 
wet  to  dry  years.  In  order  to  compare  the  merits  of  two  reservoirs 
of  about  the  same  capacity,  the  one  deep  and  the  other  shallow,  it  is 
necessary  to  determine  the  value  of  the  extra  water  saved  in  the  one 
case  and  compare  it  with  the  extra  cost  of  construction.  In  doing 
this,  due  consideration  should  be  given  to  future  irrigation  develop- 
ment and  the  probable  rise  in  the  value  of  a  water  supply. 


CHAPTER  XII 
DAM  SITES 

General  Conditions. — A  feasible  site  for  a  storage  dam  is  one 
where  topographic  conditions  are  such  that  the  outlet  from  a 
large  basin  or  valley  may  be  permanently  closed  with  a  relatively 
small  amount  of  material.  The  ideal  site  especially  for  a  high  dam 
is  one  where  solid  rock  occurs  in  the  bed  and  sides  of  a  stream  and 
where  suitable  material  for  building,  preferably  good  rock,  can  be 
obtained  in  the  immediate  vicinity.  Unfortunately  good  sites  are 
extremely  rare  and  often  the  skill  of  the  engineer  must  be  exercised 
in  making  use  of  localities  not  particularly  favorable  and  in  building 
with  such  materials  as  are  most  accessible.  From  the  ideal  condi- 
tions of  a  solid-rock  foundation  and  a  good  quarry  from  wrhich  to 
obtain  suitable  rock  for  a  dam,  he  must  usually  depart,  and  seek  to 
make  a  safe  structure  upon  a  less  firm  foundation  and  from  less 
suitable  materials.  Nearly  ideal  conditions  are  those  shown  in 
Plate  XI,  Fig.  A,  the  site  of  the  Roosevelt  Dam,  Arizona,  before  work 
was  begun. 

In  some  localities  the  depth  to  solid  rock  is  so  great  that  it  is  im- 
practicable, if  not  impossible,  to  excavate  to  it  for  a  foundation. 
Such  a  condition  may  entirely  modify  the  type  of  dam  to  be  used  and 
even  be  a  controlling  feature  in  determining  the  height  of  dam  that 
can  be  constructed.  The  fundamental  questions  concerning  a  dam 
site  are  (a)  quantity  of  material  required  for  a  dam  of  given  height ; 
(b)  material  in  foundation;  (c)  character  of  material  available  for 
construction;  (d)  conditions  for  spillway. 

It  is  also  sometimes  necessary  to  consider  the  general  location  as 
to  the  practicability  of  delivering  and  installing  the  necessary  plant 
and  equipment  for  construction.  It  is  not  until  the  above  questions 
have  been  answered  by  careful  field  examinations  that  the  feasibility 
of  any  site  can  be  established. 

Surveys  of  Dam  Site. — Having  determined  by  general  reconnais- 
sance that  a  certain  reservoir  site  is  the  best  available  for  the  storage 
of  a  given  supply  the  next  step  is  to  select  a  site  for  a  dam.  As  a  rule 
there  are  several  possible  sites  more  or  less  contiguous  to  each  other 
where  a  dam  might  be  built,  and  there  must  be  a  balancing  of  the 

190 


DAM  SITES  191 

relative  advantages  and  disadvantages  of  each.  One  location  may 
require  a  little  less  cubical  contents  for  the  dam  itself,  but  may 
require  a  deeper  foundation.  Another  may  be  nearer  the  material 
suitable  for  construction,  but  require  a  greater  cubical  content. 
For  each  of  these  sites  tentative  plans  should  be  made  and  careful 
estimates  prepared  in  order  to  weigh  their  relative  costs  and 
merits. 

The  first  steps  in  considering  a  given  site  is  to  prepare  a  careful 
topographic  map  of  it.  This  map  should  be  on  a  scale  sufficiently 
large  to  permit  quantities  both  for  the  dam  itself  and  the  foundation 
excavations  being  determined  to  a  reasonable  degree  of  accuracy. 
(See  Fig.  38.)  Ordinarily  a  scale  of  from  50  to  100  ft.  to  the  inch 
and  contour  intervals  of  from  i  to  2  ft.  are  required.  Topographic 
maps  are  not  only  valuable  in  preparing  estimates,  but  also  serve  a 
useful  purpose  in  the  laying  out  of  a  construction  plant  and  provid- 
ing for  the  handling  and  storage  of  material. 

The  most  economic  and  convenient  method  of  making  such  survey 
is  by  means  of  a  plane-table,  as  it  is  usually  possible  to  cover  the 
entire  site  from  a  few  well-chosen  stations  and  to  sketch  with  great 
accuracy  the  topography  of  all  salient  points. 

Foundation. — The  determining  factor  after  the  consideration  of 
the  general  location  of  a  dam  is  the  character  of  the  foundation. 
Upon  this  may  depend  the  height  of  dam  which  it  is  feasible  to  con- 
struct and  the  amount  of  storage  capacity  which  may  be  made  avail- 
able. While  it  is  relatively  a  quick  and  easy  piece  of  work  to  make 
the  topographic  sketches  showing  surface  features,  it  is  not  at  all  easy 
to  ascertain  the  underground  conditions  which  limit  the  character  and 
cost  of  the  structures.  In  general  it  may  be  said  that  the  foundation 
is  the  most  costly  as  well  as  the  most  vital  point  of  a  dam.  Practic- 
ally all  failures  come  either  through  lack  of  knowledge  of  the  founda- 
tion conditions  or  the  neglect  to  take  these  conditions  into  account  in 
planning  the  structure.  The  fundamental  requirements  of  a  founda- 
tion are  stability  or  bearing  power  to  carry  the  weight  of  the  dam  and 
water-tightness  to  resist  percolation  under  the  artificial  structure. 

The  bearing  power  of  a  foundation  determines  to  a  great  extent 
the  character  of  structure  which  may  be  built.  It  must  in  every 
case  be  sufficient  to  carry  the  load  imposed  upon  it  without  un- 
due settlement.  For  high  masonry  dams  a  foundation  is  required 
which  is  practically  unyielding  for  its  load,  since  settlement  especially 
under  one  part  of  the  dam  may  produce  stresses  sufficient  to  rupture 
the  masonry.  For  a  low  dam  or  one  built  of  non-consolidated  mate- 


192      PRINCIPLES  OF  IRRIGATION  ENGINEERING 

rials  which  require  great  thickness  and  width  of  base  to  sustain  the 
water  pressure  less  firm  foundations  may  be  used.  For  example  a 
dam  of  loose  rock  and  earth  may  be  safely  constructed  upon  a  founda- 
tion of  firm  earth.  In  a  structure  of  this  kind  a  slight  settlement  in 
the  foundation  is  taken  care  of  by  the  large  mass  of  non-consolidated 
material  above  gradually  assuming  a  lower  position.  Here  also  it 
is  necessary  however,  that  unequal  settlement  of  any  considerable 
magnitude  be  avoided  on  account  of  the  danger  of  opening  fissures 
in  the  dam. 

Water-tightness  as  applied  to  foundations  is  a  relative  term  as  all 
earth  and  most  rocks  are  more  or  less  porous  to  water  under  high 
pressures.  But,  hard,  compact  rock,  without  fissures  may  for 
practicable  purposes,  be  considered  as  water-tight.  In  the  most 
compact  rock,  however,  seams  or  fissures  are  frequently  found. 
Earth,  especially  that  found  in  the  bed  of  streams  or  old  waterways, 
is  likely  to  be  made  up  of  strata  of  varying  character,  some  of  which 
permit  the  passage  of  water  through  them.  While  the  existence  of  a 
semi-porous  material  in  a  foundation  may  not  be  sufficient  to  pre- 
vent its  use,  it  is  of  the  highest  importance  that  a  knowledge  be  had  of 
the  character  and  location  of  such  materials  in  order  that  suitable 
plans  may  be  prepared. 

Borings  and  Test  Pits. — The  most  complete  examination  which  it  is 
practicable  to  make  is  really  none  too  good  in  determining  the  char- 
acter of  foundation.  There  is  little  excuse  for  the  engineer  attempt- 
ing to  make  plans  for  a  dam  without  first  obtaining  full  information 
concerning  the  conditions  below  the  surface  of  the  ground.  The  cost 
of  such  examinations,  though  large,  is  not  prohibitory,  and  funds 
expended  in  this  manner  usually  result  in  the  greatest  ultimate  econ- 
omy. For  making  such  examinations  there  are  commonly  employed 
test  pits,  wash  borings  and  core  borings. 

The  simplest  and  most  common  method  of  making  examinations  in 
dry  earth  or  indurated  material  is  by  means  of  ordinary  test  pits  or 
open  wells  dug  by  hand.  In  all  parts  of  the  country  are  to  be  found 
laborers  who  have  had  experience  or  who  can  be  quickly  instructed 
in  the  matter  of  digging  and  shoring  out  the  open  hole.  Such  test 
pits  afford  access  to  the  ground  in  a  way  which  permits  very  thorough 
examination. 

It  frequently  happens  that  the  conditions  are  such  that  the  ordi- 
nary open  test  pits  cannot  be  economically  utilized  over  the  entire 
area.  This  is  especially  the  case  if  the  amount  of  water  encountered 
is  too  great  to  be  handled  by  ordinary  pumps.  It  then  becomes 


PLATE  XI 


FIG.  A. — Storage  dam  site,  Roosevelt  Dam.     Salt  River  Project,  Ariz. 


FIG.  B. — Drilling  for  bed  rock  at  storage  dam  site.     Shoshone  Project,  Wyo. 

(Facing  Page  192) 


PLATE  XI 


FIG.  C. — Spillway  of  Bumping  Lake  dam.     Yakima  Project,  Wash. 


FIG.  D. — Spillways  of  Roosevelt  Dam.    Salt  River  Project,  Ariz. 


DAM  SITES  193 

necessary  to  procure  some  form  of  apparatus  for  more  systematic 
work.  Recourse  is  usually  made  to  the  ordinary  well  diiller  who,  with 
suitable  " rig"  or  outfit  is  accustomed  to  drilling  wells  through  sand, 
gravel,  boulders,  and  solid  rock.  He  can  usually  determine  with 
reasonable  degree  of  accuracy  the  character  and  thickness  of  the  dif- 
ferent layers  or  strata,  and  if  skillful  can  shut  off  the  surface  flood  and 
ascertain  whether  the  deeper  strata  are  fissured  and  carry  consider- 
able amounts  of  water. 

Great  care  must  be  observed  in  taking  and  studying  the  material 
brought  up.  The  form  of  drill  ordinarily  employed  shatters  and 
pounds  the  rock  into  sand  or  powder  and  there  is  constant  tendency 
for  material  dislodged  from  the  upper  part  of  the  hole  to  fall  down 
and  become  mixed  with  that  which  is  being  broken  at  the  bottom. 
The  material  as  it  is  brought  up  in  a  bailer  is  washed  with  water 
in  such  way  that  the  finer  particles  are  apt  to  be  lost  and  the  samples 
examined  thus  represent  usually  the  harder  portions  of  the  rocks 
penetrated. 

Where  the  foundation  material  consists  of  rock  or  indurated  mate- 
rial, it  is  desirable  to  use  some  form  of  core  bit  for  cutting  rather  than 
the  chopping  tool  referred  to  above.  There  are  various  forms  of  core 
bit  operated  with  a  rotary  motion,  sometimes  armed  with  diamonds 
or  borts.  These  cut  away  an  annular  space,  leave  a  central  core  which 
can  be  removed  for  study.  The  softer  layers  tend  to  disappear  and 
care  must  be  exercised  in  measuring  the  depth  of  the  hole  to  account 
for  any  soft  layer  which  may  be  passed  through  and  so  completely 
ground  to  powder  as  to  be  unrecognizable.  If  a  continuous  core 
can  be  had,  this  will  furnish  a  fairly  complete  record  of  the  rocks 
penetrated. 

The  cost  of  test  pits  and  drill  holes  varies  with  the  locality.  This 
in  turn  governs  largely  the  price  of  labor  and  material.  In  general 
it  may  be  said  that  for  ordinary  test  pits  up  to  20  or  30  ft.  in  depth, 
the  cost  per  vertical  foot  is  between  $i  and  $2.  For  the  ordinary 
chopping  bit  where  holes  are  put  down  to  a  depth  of  50  or  100  ft., 
and  aggregate  possibly  a  thousand  feet  or  more,  the  cost  should  be 
approximately  the  same.  For  the  diamond  or  other  core  bit,  the 
cost  may  be  from  $3  to  $5  per  vertical  foot.  A  view  of  a  diamond 
drill  equipment  mounted  on  a  scow  at  the  Shoshone  dam  site, 
Wyoming,  is  given  in  Plate  XI,  Fig.  B. 

The  cost  per  foot  is  dependent  largely  upon  the  number  of  feet 
drilled  in  the  same  locality  as  one  of  the  principal  items  of  expense  is 
procuring,  moving  and  installing  the  apparatus.  After  it  is  once  in 

13 


194     PRINCIPLES  OF  IRRIGATION  ENGINEERING 

place  and  in  operation,  the  number  of  feet  drilled  may  be  increased 
at  will  and  the  cost  per  foot  materially  reduced. 

The  number  of  test  pits  or  borings  which  must  be  made  is,  of  course, 
dependent  upon  the  material  encountered  and  can  rarely  be  deter- 
mined in  advance,  if  for  example,  a  half  dozen  borings  are  made  at 
fairly  regular  intervals  across  the  proposed  site  and  all  show  practic- 
ally identical  results,  there  is  very  little  apparent  need  of  increasing 
the  number.  If,  however,  each  test  pit  or  boring  shows  some  different 
condition  and  gives  rise  to  suspicion  as  to  the  safety  of  the  foundation, 
then  the  number  must  be  increased  until  the  experienced  engineer 
feels  that  he  has  a  fairly  complete  knowledge  of  the  conditions. 

Character  of  Foundation. — The  character  of  materials  in  a  founda- 
tion are  as  diverse  as  are  the  components  of  the  earth's  crust. 
Passing  beneath  the  surface  cover  of  soil,  if  any,  on  the  hill  sides, 
and  of  clay,  sand,  and  gravel  of  the  river  bottom,  there  is  usually 
encountered  a  layer  of  disintegrated  material,  resulting  from  the 
weathering  of  the  underlying  rocks.  These  may  be  horizontal 
or  partly  inclined  or  even  vertical.  They  may  be  shattered,  faulty, 
or  may  be  in  thin  shaley  layers  or  in  massive  blocks.  All  of  the 
essential  facts  concerning  the  material,  its  position,  especially  its 
permeability  to  water  under  pressure,  should  be  thoroughly  under- 
stood before  the  final  plans  are  determined  upon.  The  test  pits 
or  drill  holes  should  be  continued  not  merely  into  the  firm  rock  but, 
depending  upon  the  geologic  structure,  a  few  at  least  should  be 
put  down  to  a  depth  of  100  or  more  feet,  to  be  certain  as  to  the 
still  lower  strata.  Especially  is  this  necessary  in  a  region  of  eruptive 
or  crystalline  rocks.  For  example,  there  are  instances  where  dams 
have  been  built  upon  lava  supposed  to  be  of  great  thickness,  but 
which  ultimately  proved  to  be  a  relatively  thin  shell,  with  clay 
underneath.  In  another  case,  plans  were  made  for  a  very  elaborate 
structure,  when  a  deep  drill-hole  revealed  the  fact  that  the  crystalline 
rock  on  which  a  part  of  the  dam  was  founded  was  in  reality  a  cliff 
overhanging  a  former  pocket  in  the  river  bed  and  beneath  this 
was  an  ancient  river  channel  filled  with  gravel. 

For  high  masonry  dams  where  the  loading  on  the  foundation 
is  heavy,  the  crushing  strength  of  the  rock  should  be  determined, 
especially  where  the  softer  varieties  of  rock  are  encountered. 

Character  of  Materials  for  Construction. — Having  determined 
the  character  of  materials  composing  the  foundation,  it  is  required 
next  to  ascertain  what  materials  in  the  vicinity  are  best  suited  for 
building  the  dam. 


DAM  SITES  195 

Assuming  that  the  foundation  is  of  solid  rock  it  is  highly  probable 
that  other  rock  can  be  found  in  the  vicinity  suitable  for  some  form 
of  construction.  If  so,  quarries  should  be  opened  by  experienced 
men  at  the  earliest  practicable  date  to  ascertain  the  character  and 
size  of  stone  which  may  be  had.  The  actual  opening  of  a  quarry 
has  sometimes  revealed  the  existence  of  conditions  which  have 
necessitated  an  entire  change  in  plans  or  methods  of  constructing 
the  work.  For  example,  as  the  Laguna  Dam,  on  the  Colorado 
River,  Arizona-California,  the  outer  shell  of  granite  was  firm  and 
could  be  quarried  into  large  blocks.  From  this  it  was  assumed  that 
the  rock  below  the  surface  would  be  still  better.  The  opening  of 
the  quarries,  however,  revealed  the  fact  that  the  surface  rock  was 
the  only  fair  material  available. 

If  rock  of  large  size,  weighing  a  ton  or  more  cannot  be  obtained 
economically,  the  next  consideration  is  whether  the  material  is 
suitable  for  being  crushed  and  used  in  concrete.  Where  foundation 
conditions  are  unsuitable  for  a  masonry  structure,  or  where  suitable 
rock  for  masonry  cannot  be  obtained,  consideration  must  be  given 
to  unconsolidated  material.  This  requires  a  study  of  the  problem 
of  making  a  substantial  and  water-tight  structure  of  loose  rock, 
gravel  and  earth,  or  in  some  cases  of  earth  alone.  If  an  uncon- 
solidated or  loose  structure  is  to  be  built,  the  vital  point,  so  far  as 
material  is  concerned,  is  to  find  a  clay  or  combination  of  clay  and 
sand  or  gravel  which,  when  mixed  in  proper  proportions,  is  practi- 
cally impervious  or  water  tight.  Such  a  dam  in  effect  consists 
merely  of  an  impervious  layer  properly  held  and  sustained  in  posi- 
tion, the  remaining  materials  being  simply  for  the  purpose  of  pro- 
tecting the  water-tight  portion  of  the  dam. 

In  a  timber  country,  especially  where  dams  of  a  relatively  tempo- 
rary character  are  required,  consideration  must  frequently  be  given 
to  the  use  of  wood  and  stone.  The  first  question  as  regards  material 
is  to  find  trees  of  suitable  size  and  quality  of  timber  for  supplying 
logs  for  building  cribwork,  and  next  to  this  is  the  obtaining  of  rock, 
preferably  large  stone,  for  filling  the  cribs  and  preventing  their 
being  washed  away. 

Accessibility  of  Materials  for  Construction. — Next  in  importance 
to  foundation  conditions  and  materials  for  construction  is  the 
accessibility  of  these  materials  to  the  site  of  the  work.  It  is  some- 
times the  case  that  the  best  materials  for  construction  purposes  are 
so  located  or  are  at  such  a  distance  from  the  dam  site  as  to  make 
the  cost  of  transporting  them  almost  prohibitive.  It  frequently 


196      PRINCIPLES  OF  IRRIGATION  ENGINEERING 

becomes  a  question  of  judgment  whether  it  is  preferable  to  go  to 
some  distance  from  the  work  in  order  to  obtain  the  most  suitable 
material,  or  to  attempt  to  make  a  safe  structure  from  less  favorable 
materials  which  are  found  in  the  immediate  vicinity.  In  deciding 
this  question  consideration  should  be  given  first  to  the  item  of 
safety  and  second  to  that  of  cost. 

In  determining  the  cost  of  delivery  of  material  to  the  dam,  the 
conditions  under  which  it  must  be  excavated,  length  of  haul,  charac- 
ter of  roads  and  methods  of  transportation  must  be  considered, 
The  magnitude  of  the  work  is  also  of  prime  importance  in  deciding 
what  means  of  transportation  it  is  feasible  to  employ.  For  example, 
a  plant  which  would  handle  a  million  yards  of  material  at  a  low 
unit  cost  might  result  in  very  high  unit  costs  if  used  for  one-half 
or  one-fourth  this  amount.  It  consequently  becomes  a  question  of 
determining  for  each  particular  job  the  most  economic  methods  of 
transportation. 

Before  it  can  be  said  that  material  is  accessible  to  a  given  site 
at  a  reasonable  cost  the  methods  of  transporting  the  material 
and  the  cost  of  the  equipment  required  must  be  carefully  determined. 
With  a  good  foundation  and  with  quarries  located  at  a  reasonable 
distance,  it  may  be  found  advisable  to  build  an  earth-  and  rock- 
fill  dam  rather  than  attempt  to  haul  stone  from  the  quarry  for  a 
masonry  structure. 

Spillway. — Even  of  more  immediate  importance  than  the  determi- 
nation of  the  character  of  foundations  and  materials  to  be  used  in 
constructing  the  dam  is  the  provision  for  the  safety  of  the  structure 
by  having  ample  spillway  capacity  for  the  discharge  of  excess  waters. 
This  should  be  so  planned  and  built  that  it  cannot  be  obstructed  by 
any  probable  accident,  nor  be  closed  readily  even  by  deliberate  act. 
It  is  the  safety-valve  which  insures  against  loss  of  life  and  property 
and  as  such  should  not  be  a  subject  of  any  possible  or  probable 
closure. 

The  ideal  situation  for  a  spillway  is  at  a  point  not  immediately 
contiguous  to  the  dam  where  the  water  can  overflow  in  a  broad  sheet 
and  be  collected  into  a  channel  through  which  it  may  reach  the  river 
at  a  point  sufficiently  far  below  the  dam  so  as  not  to  disturb  the 
foundations.  In  some  situations  it  is  impossible  to  find  such  a  spot 
and  the  spillway  must  be  built  on  the  natural  rock  or  soil  as  part  of 
the  dam  itself,  and  here  great  precautions  must  be  observed  to  hold 
the  water  in  check  and  to  absorb  its  energy  of  motion  in  such  way  as 
not  to  have  it  injure  the  structure. 


DAM  SITES  197 

A  criticism  which  has  been  applicable  to  many  of  the  dams  built 
in  the  past  has  been  that  the  spillways  have  not  had  sufficient 
capacity  for  the  extraordinary  floods.  Provision  has  been  made  for 
the  average  high  water,  but  the  failure  of  some  of  these  structures 
illustrates  the  fact  that  the  great  flood  of  the  century  is  one  which 
far  exceeds  the  average  high  water  and  may  occur  immediately  after 
an  ordinary  flood  has  filled  all  the  basins  and  river  channels.  The 
fact  that  the  reservoir  frequently  acts  in  such  way  as  to  absorb  most 
of  the  flood  water  and  does  not  permit  any  to  escape  tends  to  give  a 
false  sense  of  security,  or  the  fact  may  be  pointed  out  that  water  has 
never  reached  nor  filled  the  existing  spillway  and  therefore  there  is 
little  to  be  feared  that  it  ever  will.  This  is  the  fallacy  which  has 
resulted  directly  or  indirectly  in  many  catastrophes.  Succeeding 
structures  have  been  built  with  small  spillways  because  of  the  fact 
that  dams  already  erected  have  not  been  threatened  by  the  small 
capacity  already  provided.  In  this,  the  fact  is  ignored  that  the 
record  of  a  few  years  or  even  of  a  decade  or  more  is  not  to  be  relied 
upon  for  the  extraordinary  conditions  or  combinations  which  may 
occur  and  for  which  the  spillway  must  be  arranged. 

The  condition  to  be  sought  besides  those  of  safe  location  and  ample 
capacity  is  solid  rock  which  can  be  built  upon  in  such  way  as  to  form  a 
long  sill  or  weir  over  which  the  floods  may  pass.  Usually  if  rock 
exists  in  the  right  location  it  is  necessary  to  cut  this  down  to  the  de- 
sired elevation.  Occasionally  the  quarries  for  supplying  material 
for  the  dam  can  be  located  in  the  proposed  spillway,  as  at  Roosevelt, 
Arizona,  (Plate  XI,  Fig.  D)  so  as  to  make  use  of  the  material  re- 
moved. If,  however,  the  rock  is  already  too  low  it  may  be  brought 
up  to  a  proper  elevation  by  a  low  masonry  dam  forming  thus  a  sub- 
sidary  structure  to  the  main  work. 

In  some  localities,  for  example,  in  a  narrow  canyon  as  at  the 
Shoshone  Dam  in  Wyoming,  it  has  been  necessary  to  cut  a  tunnel 
through  which  the  floods  may  discharge.  In  this  case,  the  over- 
flow sill  is  constructed  on  a  curve  at  the  head  of  the  tunnel,  thus 
forming  a  broad  funnel  approach  in  which  the  water  may  be 
gathered. 

Occasionally  a  spillway  must  be  over  earth  or  gravel  or  partly 
indurated  materials  which  are  easily  worn  away  by  water.  In  such 
cases  ample  protection  must  be  provided  by  structures  preferably 
of  concrete  or  masonry  and  the  water  which  passes  over  the  spillway 
must  be  collected  in  a  channel  protected  from  backcutting  by  being 
lined  with  concrete  or  timber  (Plate  XI,  Fig.  C).  Provisions  must 


198      PRINCIPLES  OF  IRRIGATION  ENGINEERING 

also  be  made  by  means  of  chutes  or  drops  by  which  the  water  will 
expend  its  energy  internally  or  against  some  indestructible  material. 
Timber  has  occasionally  been  used  in  connection  with  spillways,  but 
the  disadvantage  is  that,  as  these  spillways  receive  water  perhaps  at 
intervals  of  many  months  or  once  a  year  or  longer,  the  wood  is  dried 
out,  warps,  or  decays,  so  that  when  brought  into  use  suddenly  the 
structure  may  fail.  For  this  reason,  as  above  stated,  concrete  or 
masonry  is  most  generally  employed. 

Records  of  Stream  Flow. — In  considering  the  size  of  spillway,  it  is 
necessary  to  have  records  of  stream  flow  not  only  giving  the  total 
amount  but  even  more  important,  the  details  of  behavior  of  individ- 
ual floods.  It  may  be  assumed  that  as  far  as  the  spillway  is  concerned 
the  flow  through  the  greater  part  of  the  year  is  insignificant,  as  it  is 
stored  in  the  reservoir,  but  the  critical  points  are  on  the  probable 
behavior  of  the  stream  at  extreme  high  water.  It  is  particularly 
important  to  know  the  intensity  of  the  flood  or  the  amount  of  water 
delivered  at  short  intervals  during  the  height  of  the  flood.  Assump- 
tions must  be  made,  based  upon  a  full  reservoir,  with  a  flood  coming 
from  the  entire  drainage  basin.  If  this  basin  is  heavily  wooded  or 
covered  with  a  thick  growth  of  bushes  and  grass,  the  rate  at  which  the 
flood  will  reach  the  reservoir  and  consequently  must  be  discharged 
over  the  spillway  may  be  assumed  as  relatively  small.  If,  on  the 
contrary,  the  drainage  basin  consists  largely  of  rock  and  uncovered 
soil,  or  is  traversed  by  roads  and  paths,  which  in  time  of  storm  act  as 
collecting  drains,  then  the  rate  at  which  the  water  will  reach  the 
reservoir  is  greatly  increased  and  hence  the  probability  of  need  of 
providing  a  large  overflow. 

Consulting  the  rainfall  records,  it  is  seen  that  a  rate  of  i  in. 
per  hour  for  the  entire  basin  is  extremely  heavy,  although  as  high 
as  3  in.  per  hour  have  been  known  in  tropical  countries.  If  the 
drainage  basin  consists  of  12,000  acres,  this  would  mean  1,000  acre- 
feet  occurring  in  an  hour  or  at  the  rate  of  500  second-feet  continued 
through  twenty-four  hours. 

In  other  words,  assuming  that  all  of  the  water  on  this  drainage 
basin  will  reach  the  reservoir  within  a  day  a  spillway  of  at  least  500 
second-feet  must  be  provided.  As  a  matter  of  fact,  however, 
much  of  this  water  might  reach  the  reservoir  in  a  shorter  time  and 
the  spillway  must  be  correspondingly  increased. 

A  large  factor  of  safety  must  always  be  employed  so  that  after 
estimating  the  largest  probable  flood,  it  is  the  part  of  wisdom  to 
multiply  this  by  two  at  least,  sometimes  by  a  larger  factor,  if  the 


DAM  SITES  199 

records  of  rainfall  or  river  flow  have  not  been  extended  over  several 
decades. 

Kind  of  Dam  Best  Adapted  to  Suit  Conditions. — From  what 
has  been  stated  above,  it  is  evident  that  the  kind  of  dam  must  be 
determined  by  the  conditions  already  discussed  of  foundation 
and  materials  available.  Plans  may  also  be  modified  in  accordance 
with  the  funds  which  are  at  hand  and  the  prospective  returns  from 
the  investment.  If  the  foundations  are  good,  that  is,  of  solid  rock 
and  quarries  of  suitable  rock  are  available,  a  masonry  structure 
may  in  general  be  considered  as  the  best,  but  something  cheaper 
may  be  allowable  if  the  financial  ability  of  the  builders  will  not 
permit  the  better  structure.  The  great  danger  in  this  connection 
lies  in  attempting  to  reduce  the  cost  below  reasonable  limits  of 
safety. 

Having  determined  upon  the  mo'st  economic  type  of  dam  and 
then  having  modified  this  to  suit  financial  requirements  and  brought 
it  to  a  minimum  of  safety  under  the  direction  of  an  experienced 
and  competent  engineer  there  is  sometimes  a  tendency  to  practise 
a  false  economy  in  the  character  of  work  and  quality  of  materials 
used  in  construction.  In  some  cases  the  work  is  entrusted  to  a 
builder,  who  in  his  desire  to  lessen  the  cost  reduces  the  dimensions 
of  the  dam  and  still  further  cuts  down  the  factor  of  safety.  This 
has  been  the  cause  of  several  failures;  the  plans  were  modified  by 
experienced  men  to  a  point  where  they  could  no  longer  permit 
further  reductions  of  cost  and  then  the  work  was  entrusted  to  men 
who  still  further  cut  down  the  requirements,  not  letting  it  be  known, 
however,  that  the  approved  plans  were  being  changed  in  detail. 
These  changes  were  not  discovered  until  after  some  catastrophe 
had  occurred  and  the  question  was  raised  as  to  whether  the  dam 
had  been  correctly  designed  or  a  proper  type  of  structure  adopted. 


CHAPTER  XIII 
TIMBER  DAMS 

Kinds  of  Dams. — A  dam  is  an  obstruction  placed  across  a  stream 
or  depression  and  so  devised  as  to  hold  back  or  obstruct  the  flow  of 
the  water.  It  may  be  built  in  such  way  that  water  will  flow  over 
it,  in  which  case  it  is  termed  an  overflow  or  submerged  dam  or  weir; 
or  it  may  be  of  such  height  that  it  cannot  be  overtopped.  In  the 
latter  case,  if  relatively  long  and  low,  it  may  be  termed  a  dike  or 
levee. 

The  essential  feature  of  any  dam  is  the  relatively  impervious 
layer,  curtain  or  blanket  held  in  place  by  a  suitable  arrangement 
of  material.  The  whole  structure  may  be  impervious  or  only  a 
thin  section  of  it  either  in  the  interior  or  against  the  upper  or  water 
face.  The  material  which  holds  this  impervious  layer  in  place  may 
be  of  wood  such  as  logs  or  of  earth  properly  compacted,  of  stone  either 
loose,  or  carefully  laid,  of  concrete,  brick,  steel,  or  almost  any  other 
building  material. 

This  material  may  be  arranged  simply  as  a  great  mass  dumped 
in  together  or  may  be  carefully  proportioned  and  built  to  secure 
the  greatest  economy  of  material,  following  the  rules  laid  down 
by  scientific  observation  of  the  strength  of  materials  and  deductions 
based  upon  mathematical  principles. 

Dams  are  classified  according  to  the  material  of  construction  and 
its  arrangement  in  the  structure.  One  form  grades  by  insensible 
degrees  into  another,  but  the  following  may  be  distinguished: 

Timber  dams,  including  brush  dams  and  log  or  crib  dams. 

Earth  dams. 

Rock-fill  dams. 

Rock  and  earth-fill  dams. 

Masonry  dams. 

Early  Stages  of  Development. — The  most  elementary  form  of  dam, 
so  far  as  known,  is  that  constructed  by  the  beavers  or  their  relatives. 
Examples  of  the  work  of  these  animals  are  to  be  found  in  various 
sections  of  the  country  and  the  rude  skill  displayed  by  them  in  using 
timber  and  earth  and  stone  to  form  an  obstruction  for  holding  up 

200 


TIMBER  DAMS  201 

small  heads  of  water  causes  us  to  question  whether  it  is  not  from  them 
that  man  learned  his  first  lesson  in  this  branch  of  engineering. 

The  early  dams  built  by  men  were  constructed  of  small  logs  and 
brush,  and,  like  the  beaver  dams,  were  arranged  in  such  a  way  as  to 
have  the  branches  interlaced  so  as  to  form  a  more  or  less  systematically 
interwoven  mat  or  rude  fence.  Man  learned  to  improve  upon  these 
methods  by  holding  the  light  material  in  place,  and  prevent  its  being 
floated  away  by  means  of  loose  rock.  Larger  logs  were  also  soon 
used,  these  being  arranged  more  and  more  regularly  until  by  degrees 
there  was  an  evolution  from  the  irregular  brush  and  stone  dam  to  the 
systematical  dam  in  which  the  logs  are  arranged  in  geometrical  forms 
with  the  spaces  between  filled  with  carefully  placed  rocks,  both  large 
and  small. 

In  the  earlier  stages  of  irrigation  the  brush  and  stone  dam  was 
largely  used  for  diverting  water  from  the  stream  into  the  canal  as 
shown  in  Plate  XII,  Fig.  A.  For  the  small  irrigation  systems  where 
each  canal  supplied  water  to  but  a  few  farms,  it  was  by  far  the  most 
economic  structure  that  could  be  used.  At  high  water  it  was  usually 
wholly  or  in  part  washed  away,  but  this  did  not  result  in  any  notice- 
able loss.  After  the  stream  subsided  in  summer  so  that  the  water 
no  longer  flowed  freely  into  the  head  of  the  canal,  the  farmers 
assembled,  cut  the  necessary  brushes  from  the  adjacent  banks  of  the 
stream,  floated  these  into  position  and  secured  the  mat  thus  made  by 
placing  boulders  and  small  stone  upon  it.  In  plan,  the  dam  was 
usually  placed  diagonally  up-stream  from  the  intake  of  the  canal 
so  as  to  force  the  current  directly  toward  it. 

Improvements  on  this  rude  form  were  later  made  by  tying  the  brush 
together  with  wire  and  anchoring  it  to  posts.  As  the  water  still 
further  subsided,  the  dam  was  made  more  nearly  water  tight  by 
throwing  gravel,  sand  and  earth  against  its  upper  side.  The  total 
outlay  of  time  and  labor  required  for  this  work  was  not  usually  great 
and  the  annual  cost  of  replacement  less  than  the  interest  and  depreci- 
ation on  a  more  permanent  structure. 

After  crop  production  and  land  value  increased  a  point  was  reached 
when  it  was  not  economy  to  repair  these  dams  annually,  or  after  each 
flood,  and  consideration  was  given  to  a  more  permanent  form  of 
structure,  one  which  did  not  necessitate  men  leaving  their  farms  at 
the  critical  time  of  crop  seasons  for  the  purpose  of  making  repairs. 
It  also  frequently  happened  that  the  inlet  of  the  canal  was  at  such  a 
height  above  the  bed  of  the  stream  that  the  brush  dam  was  not 
sufficient  to  force  the  low  water  flow  up  to  it.  In  that  case,  a  struc- 


202      PRINCIPLES  OF  IRRIGATION  ENGINEERING 

ture  was  required  which  would  raise  the  water  and  which  would  be 
strong  enough  to  resist  the  floods.  The  next  step  was  therefore  the 
consideration  of  a  dam  built  of  more  substantial  materials.  It  is  thus 
seen  that  the  timber  dam  is,  to  a  certain  extent,  the  outgrowth  of 
more  systematic  arrangement  of  the  same  class  of  material  used  in 
the  brush  and  stone  dam.  One  of  the  intermediate  types  of  dam  is 
shown  in  Plate  XII,  Fig.  B. 

Use  of  Timber  Dams. — In  regions  where  timber  is  plentiful  and 
consequently  cheap,  timber  or  timber  and  stone  dams  are  extensively 
used.  As  a  rule  this  use  is  confined  to  diversion  wiers  or  submerged 
obstructions  the  water  flowing  over  them  at  all  times  when  there  is  a 
sufficient  supply  in  the  stream.  In  some  cases  timber  dams  are  also 
used  for  storage  reservoirs  where  comparatively  low  heads  are 
required. 

Where  wood  is  exposed  to  both  wet  and  dry  conditions,  its  tendency 
to  decay  is  rapid.  For  this  reason  timber  dams  used  in  streams 
which  are  dry  during  a  portion  of  the  year,  or  where  there  is  a  wide 
variation  of  head  against  them  must  be  considered  as  temporary  in 
character.  The  conditions  which  will  justify  the  construction  of  a 
temporary  structure  of  this  kind  will  vary  in  each  particular  case  and 
locality. 

Where  Timber  Dams  are  Applicable. — Timber  dams  are  applicable 
for  practically  all  conditions  where  a  low  head  (20  ft.  or  less)  is  re- 
quired and  where  there  are  suitable  materials  available  at  reasonable 
cost  for  their  construction.  The  principal  materials  required  are  logs, 
either  rough  or  sawed  into  square  timbers  or  planks,  and  stone  vary- 
ing in  size  up  to  200  lb.,  or  even  more.  They  are  especially  adapted 
to  regions  where  trees  of  suitable  size  and  quality  for  logs  can  be  cut 
on  the  upper  reaches  of  the  stream  and  floated  into  position. 

Timber  dams  may  be  adapted  to  practically  any  kind  of  founda- 
tion conditions,  from  solid  rock  to  comparatively  soft  earth,  by 
giving  them  sufficient  width  of  base  and  using  cut-off  walls  where 
required  to  avoid  percolation  under  the  dam.  Except  on  solid-rock 
foundation,  it  is  necessary  also  to  protect  the  lower  toe  from  erosion 
and  undermining  the  structure.  If  properly  constructed  their  safety 
is  not  endangered  by  slight  settlements,  and  for  this  reason  the  tim- 
ber dam  may  be  constructed  on  a  foundation  which  would  be  unsuit- 
able for  a  less  elastic  structure,  such,  for  example,  as  masonry.  (See 
Plate  XII,  Figs.  A  and  B.) 

The  plan  of  the  dam  may  be  straight  or  curved,  and  built  at 
right  angles  to  the  current  or  diagonally  with  it.  The  latter  plan 


PLATE  XII 


FIG.  A. — Brush  and  stone  dam,  typical  of  pioneer  conditions. 
Rio  Grande,  N.  Mex. 


Las  Cruces  canal, 


FIG.  B. — Log  and  earth  dam. 


Cimarron  River,  N.  Mex. 

(Facing  Page  202) 


PLATE  XII 


FIG.  C. — Foundations  for  timber  dam.     Yakima  Project,  Wash. 


FIG.  D. — Apron  of  partly  finished  timber  dam.     Yakima  Project,  Wash. 


TIMBER  DAMS  203 

is  sometimes  used  in  order  to  increase  the  length  of  overflow  and 
decrease  the  depth  of  water  on  the  crest.  In  this  case  there  is  a 
tendency,  however,  to  force  the  stream  toward  one  bank,  with 
consequent  danger  of  erosion,  or  if  directed  toward  the  intake  of 
the  canal,  with  liability  of  throwing  the  floods  into  the  head  and 
bringing  in  large  quantities  of  sand,  gravel  and  debris. 

A  curved  plan  of  timber  dam  has  occasionally  been  used  in  order 
to  gain  the  advantage  of  the  effect  of  the  arch.  The  water  pressure 
against  the  up-stream  face  putting  the  structure  in  compression. 
The  gain  in  this  respect  is  not  very  great,  but  is  worthy  of  con- 
sideration if  the  abutments  are  sufficiently  firm. 

Conditions  of  Stability. — Unlike  a  masonry,  concrete  or  similar 
rigid  structure,  a  timber  dam  is  not  dependent  for  stability  on  each 
part  being  held  by  friction  or  by  the  resistance  due  to  cohesion  of  the 
various  parts.  On  the  contrary,  it  is  essentially  a  wooden  frame 
tied  together  in  such  a  way  as  to  be  moderately  elastic  and  held 
from  floating  or  sliding  by  its  loading  of  rock,  which  in  turn  is  held 
in  place  by  the  network  of  timbers.  This  sort  of  structure  allows  a 
certain  amount  of  settlement  or  sliding  and  an  adjustment  under 
pressure  of  gravity  so  that  a  change  in  position  which  might  be 
fatal  to  almost  any  other  form  of  dam  may  tend  to  strengthen 
rather  than  weaken  the  structure. 

Timber  dams  are  sometimes  also  built  with  such  an  up-stream 
slope  that  the  weight  or  downward  pressure  of  the  water  tends  to 
hold  them  firmly  on  the  foundation  so  that  the  added  weight  of 
water  with  increased  head  tends  to  strengthen  the  factor  of  safety 
against  sliding. 

The  principal  features  to  be  safeguarded  in  the  construction  of 
timber  dams  are: 

(a)  Protection  against  sliding  on  the  foundation. 

(b)  Bonding  together  of  the  various  timber  elements. 

(c)  Protection  against  undermining. 

Sliding  on  the  foundation,  as  heretofore  mentioned,  is  provided 
against  by  weighting  the  structure  by  means  of  heavy  rock,  and  in 
some  cases  also  by  constructing  the  up-stream  slope  at  such  an  angle 
that  the  weight  of  the  water  exerts  a  vertical  component  through 
the  dam  on  its  foundation.  The  holding  of  the  dam  together  may 
be  accomplished  by  means  of  drift  bolts  driven  through  the  various 
timbers  so  as  to  securely  tie  them  together  at  each  point  of  junction. 

The  dam  may  be  protected  against  undermining,  if  it  be  on  other 
than  solid-rock  foundation,  by  carrying  an  apron  for  some  distance 


204      PRINCIPLES  OF  IRRIGATION  ENGINEERING 

down-stream  below  the  lower  tow.  It  is  necessary  also  to  give 
protection  against  cutting  around  the  abutments  by  constructing 
the  dam  well  into  the  banks  or  providing  masonry  abutments 
against  which  it  may  rest. 

Additional  strength  is  sometimes  given  to  timber  dams  by  con- 
structing them  either  in  the  form  of  an  arch  or  "  V"  shape.  Dams 
built  in  this  form  must  have  solid  banks  against  which  the  ends  may 
rest,  or  masonry  bulkheads  should  be  constructed.  If  artificial 
abutments  are  used,  they  should  be  carried  up  above  the  flood 
line  of  the  stream. 

Water-tightness. — Timber  dams  are  made  water-tight,  or  nearly 
so,  by  means  of  a  tight  facing  of  either  earth  and  gravel  or  of  wood. 
This  water-tight  facing  should  be  located  at  the  up-stream  face  of 
the  dam.  In  general,  it  is  believed  that  a  water-tight  facing  of  earth 
and  gravel  is  superior  to  that  of  lumber  on  account  of  its  greater 
lasting  qualities,  and  also  its  tendency  to  remain  tight  under  low- 
water  conditions. 

The  interior  spaces  of  the  dam  should  be  filled  with  loose  rock  and 
where  available,  gravel  should  be  carefully  packed  around  the  various 
timber  members  in  order  to  further  protect  them  from  decay.  The 
interior  of  the  dam  should  be  sufficiently  porous  that  water  which 
may  find  its  way  through  the  water-tight  face  will  be  quickly 
drained  away. 

Types  of  Timber  Dams. — Various  types  of  timber  dams  have 
been  successfully  used  and  it  is  impossible  to  say  that  any  one  type 
is  superior  to  another.  Each  particular  design  should  be  made  to 
suit  local  conditions  of  foundation  and  material  available  for  con- 
struction, for  example,  in  a  locality  remote  from  mills,  a  design 
adapted  to  the  use  of  round  logs  would  be  probably  more  economical 
than  one  of  sawed  timbers,  even  though  the.  amount  of  material 
required  in  the  former  case  was  greater  than  in  the  latter.  On  the 
other  hand,  in  a  locality  where  timber  is  less  plentiful  and  where 
dimension  lumber  can  readily  be  gotten,  a  saving  might  be  effected 
by  using  sawed  timbers  and  so  designing  the  structure  as  to  require 
the  minimum  amount. 

Practically  all  of  the  different  types  of  timber  dams  depend  upon 
the  principles  heretofore  given  for  stability  and  water-tightness. 

Among  the  more  common  types  of  timber  dam  which  may  be 
mentioned  are  log  and  brush  dams,  crib  dams,  combination  crib 
and  pile  dams,  and  framed  dams. 

Log  and  Brush  Dams. — This  type  of  dam  is  well  suited  to  local- 


TIMBER  DAMS  205 

ities  where  timber,  preferably  long  trees,  can  be  obtained  without 
difficulty.  It  consists  essentially  of  a  series  of  mats  of  logs  of  various 
lengths  laid  in  the  stream  parallel  with  the  current.  The  tops  of  the 
trees  in  each  case  being  placed  up-stream.  At  the  lower  face  of  the 
dam  the  various  layers  of  mats  are  separated  by  means  of  one  or 
more  rows  of  fairly  uniform  sized  logs  carried  crosswise.  This  has 
the  effect  of  building  up  the  lower  portion  of  the  dam  more  rapidly 
than  that  portion  further  up-stream,  and  giving  a  long  flat  slope  to 
the  upper  face  as  shown  on  Plate  XII,  Fig.  B.  The  horizontal  and 
longitudinal  timbers  which  form  the  lower  face  of  the  dam  should  be 
securely  fastened  together  by  means  of  drift  bolts,  or  otherwise. 

In  a  dam  of  this  kind  a  thin  layer  of  gravel  and  fine  brush  should 
be  placed  between  the  various  courses  of  the  timbers  and  the  struc- 
ture should  be  given  weight  and  stability,  as  well  as  water-tightness 
by  covering  the  up-stream  face  with  earth,  loose  rock  and  gravel. 

It  is  well  to  allow  the  first  two  or  three  courses  of  timbers  to 
project  some  distance  down-stream  below  the  toe  of  the  main  dam, 
thus  forming  an  apron  for  protection  against  erosion.  For  a  dam 
of  moderate  height,  say  from  8  to  10  ft.,  the  first,  or  bottom  layer  of 
timbers  should  project  down-stream  from  20  to  30  ft.,  the  second 
layer  from  10  to  15  ft.  and  the  third  layer  from  5  to  8  ft. 

Crib  Dams. — This  form  of  dam  consists  essentially  of  a  series  of 
timber  cribs  built  up  across  the  stream  and  filled  with  loose  rock  to 
prevent  their  being  washed  away.  These  cribs  are  commonly  built 
of  either  round  or  sawn  timbers.  They  may  also  be  built  of  various 
shapes  and  sizes,  depending  upon  the  material  available  and  the 
height  of  dam  required.  (See  Plate  XII,  Figs.  C  and  D.) 

A  common  form  of  crib  dam  consists  of  a  series  of  rectangular 
cribs  from  10  to  15  ft.  square  carried  in  a  straight  line  across  the 
stream.  Where  the  foundation  is  of  solid  rock  it  is  a  common  practice 
to  excavate  into  the  rock  sufficient  to  receive  the  first  row  of  timbers. 
The  first  or  second  layer  of  timbers  from  the  foundation  are  usually 
laid  close  together  so  as  to  form  a  floor  in  each  of  the  cribs  for 
holding  the  rock.  The  timbers  are  all  securely  fastened  to  each 
other  at  their  junctions  by  means  of  drift  bolts  or  pins.  Water- 
tightness  is  secured  by  means  of  a  facing  of  gravel  and  earth,  or  some- 
times of  planking. 

An  apron  for  protecting  the  lower  toe  of  the  dam  in  case  of  floods 
is  frequently  made  by  constructing  a  second  row  of  low  cribs  below 
the  main  dam  and  filling  them  with  rock. 

In  other  forms  of  dams  the  cribs,  instead  of  being  built  up  verti- 


206      PRINCIPLES  OF  IRRIGATION  ENGINEERING 


TIMBER  DAMS 


207 


I 


cally,  are  inclined  on  the  up-stream  or  down-stream  face 
thus  giving  a  triangular  section. 
A  crib  with  the  inclined  face  up- 
stream has  the  advantage  of  util- 
izing the  downward  pressure  of 
the  water  in  producing  a  greater 
degree  of  stability.  Also,  one 
with  an  inclined  down-stream 
face  tends  to  carry  the  overflow 
in  time  of  floods  away  in  a  more 
nearly  horizontal  direction  and 
with  less  liability  of  erosion  at 
the  toe  than  is  the  case  when  the 
fall  is  vertical. 

Crib  and  Pile  Dams. — A  com- 
mon form  of  dam  and  one 
adapted  to  a  soft  bottom,  which 
does  not  contain  quicksand,  is 
the  combination  of  driving  piles 
and  against  these  building  the 
crib  work. 

Two  or  more  rows  of  piles  are 
driven  directly  across  the  river  at 
right  angles  to  the  current.  The 
cribs  are  then  constructed  between 
the  rows  of  piling  and  filled  with 
rock  or  rock  and  brush.  As  an 
illustration  of  this  type  of  dam, 
is  that  on  Yellowstone  River, 
Montana,  below  Glendive,  a  part 
plan  of  which  is  given  in  Fig.  39, 
together  with  location,  plan  and 
cross-section  of  the  river. 

In  Fig.  40  is  given  the  cross-sec- 
tion of  the  dam  showing  the  rela- 
tive position  of  the  piles  and  the 
braces,  with  apron  and  protecting 
rock  below. 

A  modification  of  this  form 
is  to  drive  a  double  row  of 
piles  across  the  stream  with  a 


or  both, 


3S. 


208      PRINCIPLES  OF  IRRIGATION  ENGINEERING 

clear  space  of  about  2  ft.  between  them.  The  piles  in  each  TOW 
are  placed  immediately  above  and  below  each  other  and  spaced 
the  same  distance  apart  as  the  two  rows  are  distant  from  each 
other.  These  spaces  between  the  piles  are  then  filled  with  logs 
built  up  crib  fashion  and  laid  at  right  angles  to  each  other.  The 
logs  parallel  to  the  direction  of  the  current  are  allowed  to  project 
some  distance  up-stream  so  as  to  form  the  upper  face  of  the  dam,  and 
terminating  on  the  lower  side  just  below  the  lower  row  of  piling. 
Care  must  be  taken  in  driving  the  piles  so  as  not  to  permit  the  river  to 
scour  out  the  bottom  between  them,  and  thus  permit  a  current  to  get 
started  under  the  crib  work.  Protection  of  the  bottom  during  the 
driving  of  the  piles  and  construction  of  the  dam  may  in  some  cases  be 
secured  by  means  of  brush  mattresses.  Where  this  cannot  be  done  it 
is  sometimes  advisable  to  first  float  the  cribs  into  position  and  then 
drive  the  piles  through  the  cribs,  the  latter  serving  to  protect  the 
bottom  from  erosion. 

Framed  Dams. — The  frame  type  of  dam  requires  far  less  timber 
than  the  ordinary  log  or  crib  dams  heretofore  described.  For  this 
reason  it  is  better  adapted  to  localities  where  timber  is  scarce.  For 
convenience  in  framing  the  timber  should  be  sawed  to  regular 
dimensions. 

The  dam  consists  essentially  of  framed  timber  bents  placed 
parallel  with  the  current.  The  bottom  timbers  of  the  bents  are 
fastened  to  cross  sills  set  into  the  foundation  and  securely  anchored. 
Where  the  foundation  is  on  rock  the  anchorage  may  be  made  by 
means  of  iron  bolts  split  at  the  lower  end  and  wedged  into  holes 
drilled  in  the  rock. 

The  upper  face  of  the  dam  should  be  inclined  at  an  angle  sufficient 
that  the  vertical  component  of  the  water  load  will  act  as  a  weight  to 
prevent  sliding. 

Water- tightness  is  ordinarily  secured  by  means  of  a  plank  face 
on  the  upper  slope  of  the  dam.  The  interior  spaces  between  the 
bents  are  in  general  filled  with  loose  rock  to  give  the  structure  greater 
stability,  although  this  is  not  absolutely  necessary,  safety  being 
insured  by  the  strength  of  the  bents  and  the  water  load  on  the  flat 
upper  face. 

The  lower  toe  should  be  protected  by  means  of  an  apron  carried 
well  down-stream.  Trie  lower  end  of  this  apron  should  be  further 
protected  by  means  of  piling  or  rock.  The  force  of  the  water  may 
also  be  broken  by  constructing  the  lower  face  of  the  dam  in  steps 
or  on  an  incline. 


TIMBER  DAMS 


209 


A  layer  of  loose  rock  or  earth  and  gravel  should  be  placed  on  the 
upper  face  of  the  dam  for  some  distance  above  the  toe  or  in  place 
of  this  a  mass  of  concrete  making  a  more  permanent  structure  as 
shown  in  Fig.  41. 


Upper  Approach 
Excavated  to  Elev.2302 


2-8  Boat  Spikes 
to  each  Log 
Elev.2299 


Section  of  Dam 
15' 


6  Hewn  Timbers  16' Long,  Laid  Close 
and  Secured  to  Logs  with  2- H"x  12" 
Boat  Spikes  at  each  Intersection 


Bottom  of  Concrete 
Bottom  of  Stone  Filling 

All  Logs  12'ln  Dia.at  the  Butt. 

Log  Drift  Bolts  1'Bd.  20"Long. 


B~*  Billed  with  Plan  of  Dam 

Selected  Material  /  „ 


^20^04,204,120^20 


6  Hewn  Timbers 
6' Long.  Laid  2" 
apart,  and  Secured 
to  Logs  with  2  - 

10"Boat 

Spikes  at  each 
Intersection 


South  Abutment 


FIG.   41.  —  Concrete,     rock 


and     timber    diversion    dam,    Yakima    Project, 
Washington. 


Limits  of  Height.  —  The  height  to  which  timber  dams  may  be  built 
is  limited  largely  by  the  character  of  the  foundation  and  quality  of 
material  available.  There  are  examples  of  timber  dams  with 

14 


210      PRINCIPLES  OF  IRRIGATION  ENGINEERING 

heights  of  from  30  to  40  ft.,  or  even  greater,  which  have  stood  for 
years.  On  a  firm  rock  bed  not  easily  eroded  and  with  heavy  long 
logs  and  large  stone  there  is  no  reason  why  even  these  heights 
should  not  be  exceeded. 

Ordinarily  the  use  of  timber  dams  is  limited  to  low  heads,  gener- 
ally not  exceeding  1 5  or  20  ft.  For  such  heads  cribs  may  be  built 
of  logs  or  planks  floated  into  position  if  the  water  is  sufficiently  deep, 
loaded  with  rocks  and  the  work  carried  on  with  a  reasonable  degree 
of  safety.  For  higher  structures  a  greater  degree  of  protection  in 
their  building  is  necessary. 

On  account  of  the  temporary  character  and  the  possibility  of 
failure  after  a  few  years  of  service,  timber  dams  cannot  be  strongly 
recommended  for  high  heads  or  for  localities  where  any  large  quantity 
of  water  is  to  be  held  in  storage.  For  diversion  weirs  and  low  dams, 
especially  in  localities  where  timber  is  cheap  they  frequently  are  the 
most  economic  form  of  dam  that  can  be  adopted. 


CHAPTER  XIV 
EARTH  DAMS 

Site  for  Earth  Dam. — The  site  usually  chosen  for  an  earth  dam 
is  of  such  a  character  that  the  building  of  a  masonry  structure  upon 
it  is  impracticable.  Frequently  solid  rock  foundation  conditions 
do  not  exist,  or  even  where  such  conditions  do  exist  suitable  materials 
for  the  building  of  a  masonry  dam  may  not  be  available  in  the 
immediate  vicinity.  A  firm  rock  foundation  is  as  desirable  for  an 
earth  dam  as  it  is  for  any  other  type.  It  is,  however,  possible  to 
build  an  earth  dam  upon  unconsolidated  materials  such  as  are 
usually  found  in  river  valleys  and  consisting  of  clays,  sands  and 
gravels  with  occasional  boulders.  It  is  also  possible  to  use  for  the 
body  of  an  earth  dam  materials  that  are  commonly  found  convenient 
to  any  site  which  may  be  selected. 

On  account  of  the  conditions  above  stated  possible  sites  for  earth 
dams  are  far  more  common  than  those  suitable  for  masonry  struc- 
tures. It  is  not  to  be  assumed,  however,  that  all  possible  sites  are 
equally  satisfactory,  or  that  any  which  can  be  found  in  a  particular 
locality  are  ideal.  The  choice  of  a  site  is  frequently  a  matter  of 
compromise  between  alternatives  any  one  of  which  may  be  made  to 
serve  the  purpose  but  none  of  which  are  particularly  attractive. 
It  is  usually  possible  to  find  points  of  criticism  for  every  site  as  well 
as  for  the  type  of  structure  best  suited  to  it.  The  choice  is  there- 
fore not  between  locations  offering  superior  advantages  but  rather 
between  those  possessing  disadvantages  which  should  be  avoided. 

Foundation. — One  of  the  principal  requirements  for  the  foundation 
of  an  earth  dam  is  that  it  shall  be  practically  water  tight  below  the 
lower  point  of  the  structure.  It  is  essential  also  that  the  material 
be  firm  enough  to  sustain  the  load  which  is  imposed  upon  it.  The 
latter  condition  is  less  likely  to  give  trouble  than  the  former,  and 
there  is  probably  no  one  question  of  more  importance  in  connection 
with  earth  dams  than  that  of  the  water- tightness  of  the  material 
upon  which  they  are  built. 

As  a  rule  the  surface  and  sub-surface  materials  have  been  laid 
down  by  running  water  which  results  in  their  being  stratified  or 
consisting  of  alternate  layers  of  clay,  sand  or  gravel  of  various 

211 


212      PRINCIPLES  OF  IRRIGATION  ENGINEERING 

degrees  of  coarseness.  These  layers  of  pervious  materials  may 
consist  of  small  horizontal  courses  entirely  sealed  within  a  thick 
impervious  clay  stratum.  Or  they  may  extend  for  several  hundred 
or  even  a  thousand  feet  and  terminate  in  some  open  channel  or  near 
the  surface  of  the  ground  below.  Water  entering  one  of  these  sheets 
or  layers  of  gravel  may  percolate  slowly  through  it  and  escape  at 
lower  or  more  pervious  points.  Where  such  conditions  exist  it  is 
essential  that  they  be  known  and  that  provisions  be  made  to  prevent 
water  in  any  quantity  percolating  under  the  dam. 

Occasionally,  the  foundation  consists  of  rock  disintegrated  in 
place  and  which  has  not  been  rearranged  by  flowing  waters.  In 
this  case,  there  is  no  definite  sorting  of  the  sub-surface  material, 
but  this  is  often  loose  or  porous,  because  of  the  solution  and  removal 
of  the  more  soluble  particles  of  rock,  thus  water  may  pass  freely 
through  it  or  along  the  old  bedding  planes.  Under  other  conditions 
the  foundations  may  be  partly  filled  with  material  which  has  rolled 
in  from  the  sides,  such  as  boulders  and  smaller  debris,  the  latter 
partly  rearranged  by  the  occasional  floods  but  still  quite  pervious  to 
water.  Too  great  care  cannot  be  urged  in  determining  the  character 
of  the  foundation  materials  especially  under  high  dams.  Where 
these  are  porous  or  otherwise  unsatisfactory  precautionary  measures 
sufficient  to  insure  the  safety  of  the  structure  must  be  taken. 

Selection  Of  Materials. — The  materials  to  be  used  in  an  earth 
dam  are  governed  largely  by  the  character  of  those  found  in  its 
immediate  vicinity.  It  is  usually  not  practicable  to  bring  the  earth 
for  large  structures  from  long  distances  excepting  possibly  a  small 
amount  of  clay  or  other  impervious  substance.  The  selection 
of  materials  for  a  dam  is  therefore  usually  confined  to  a  choice 
from  one  or  two  localities  frequently  where  the  formation  is  not  ideal. 
The  location  of  suitable  earth  for  forming  a  water-tight  embank- 
ment may  govern  to  some  extent  the  selection  of  the  site  for  a  dam. 

The  first  and  prime  requisite  for  the  filling  for  an  earth  dam  is 
water-tightness  and  next  to  this  stability.  Finely  divided  substances 
such  as  silts  and  clays  are  the  most  nearly  water  tight,  but  frequently 
do  not  possess  the  necessary  qualities  for  being  compacted  into  a 
firm  embankment.  Gravel  containing  a  small  amount  of  fine 
material  is  capable  of  being  so  compacted  but  does  not  possess  the 
requisite  quality  of  water-tightness.  The  ideal  combination  is  one 
composed  of  gravel,  sand  and  finely  divided  earth  such  as  silt 
or  clay  in  such  proportions  as  to  make  a  stable  yet  impermeable 
mixture.  To  meet  this  requirement  the  spaces  between  the  larger 


EARTH  DAMS  213 

particles  must  be  filled  and  the  volume  of  voids  reduced  to  a  mini- 
mum, and  yet  with  the  component  particles  of  such  size  that  they 
will  not  slide  freely  upon  each  other. 

Occasionally,  though  rarely,  this  combination  is  found  in  nature, 
but  more  often  it  is  necessary  to  combine  materials  taken  from 
different  localities.  In  order  to  do  this  it  is  necessary  to  make  a 
mechanical  analysis  of  those  available  and  combine  them  in  the 
proper  proportions  to  obtain  the  desired  results.  Where  such 
mechanical  mixtures  are  necessary  constant  vigilance  must  be 
exercised  during  the  progress  of  the  work  in  order  to  have  at  all 
times  the  proper  combination.  This  is  especially  true  for  the  im- 
pervious or  up-stream  portion  of  the  dam. 

Section  of  Dam. — The  top  width  and  external  slopes,  or  cross- 
section  of  an  earth  dam  is  governed  by  somewhat  arbitrary  rules 
based  upon  experience  in  structures  which  have  stood  the  test  of 
time.  On  acount  of  the  varying  conditions  of  saturation  and  friction 
in  different  materials,  there  is  no  known  law  by  which  the  resistance 
of  an  earth  dam  can  be  computed.  As  a  rule,  the  slope  on  the  up- 
stream or  water  face  is  made  less  steep  than  that  on  the  down- 
stream or  dry  side,  because  of  the  fact  that  the  saturation  leads  to  a 
tendency  to  slide  or  slough,  especially  when  the  water  is  being  drawn 
down  in  the  reservoir. 

For  the  upper  or  wetted  slope  the  minimum  is  about  three  hori- 
zontal to  one  vertical,  although  there  are  cases  where  a  less  slope  has 
been  chosen  when  this  could  be  drained  and  protected  by  a  suitable 
covering  or  by  a  paving  of  heavy  rock.  Dams  have  been  constructed 
with  an  up-stream  slope  of  5  to  i  although  3  1/2  or  4  to  i  is  as  flat  as 
are  commonly  used. 

For  the  lower  face,  the  minimum  slope  is  usually  2  or  2  1/2  to  i. 
Occasionally,  this  is  broken  by  horizontal  berms  or  benches  which 
serve  to  break  the  smooth  face,  give  greater  thickness  to  the  base, 
provide  convenient  location  for  surface  drains,  and  for  roadways 
affording  access  to  various  parts  of  the  structures. 

The  top  width  is  rarely  made  less  than  10  ft.  for  low  structures 
say  up  to  30  ft.  in  height  and  for  dams  over  this  height  is  ranges  from 
i o  to  30  ft.,  20  ft.  being  the  width  commonly  used. 

Prevention  of  Seepage  under  Dam. — The  points  where  the  arti- 
ficial structure  joins  or  is  placed  upon  the  original  earth  or  rock  are 
those  to  which  most  care  should  be  given  as  along  this  line  of  contact 
water  under  pressure  usually  finds  most  ready  access  and  passage. 
Great  percautions  must  therefore  be  taken  in  preparing  the  founda- 


214      PRINCIPLES  OF  IRRIGATION  ENGINEERING 

tions  and  in  arranging  a  junction  such  as  to  prevent  or  reduce  the 
amount  of  seepage  along  this  plane.  Such  seepage  is  checked  or 
prevented  usually  by  providing  a  cut-off  trench  or  wall,  extending 
deep  into  the  foundations,  this  being  extended  or  sometimes  replaced 
by  one  or  more  rows  of  sheet  piling  driven  as  deep  as  practicable. 

The  ground  to  be  occupied  by  the  dam  should  be  carefully  cleaned 
of  all  stumps,  roots  or  other  organic  matter  liable  to  decay  and  all 
of  the  loose  soil  removed  down  to  a  depth  of  a  foot  or  more  beneath 
the  surface,  this  depth  being  dependent  upon  the  character  of  the 
ground.  If  the  sub-soil  is  firm  and  free  from  roots  or  holes  of 
burrowing  animals,  the  depth  of  the  stripping  may  be  reduced  but 
in  general  it  is  better  to  be  on  the  safe  side,  and  uncover  the  entire 
proposed  base  of  the  dam  to  a  depth  below  where  the  soil  shows  the 
effects  of  penetration  by  roots  and  of  weathering. 

The  material  stripped  off,  if  containing  a  loam,  should  be  placed 
at  one  side  out  of  the  way  for  use  later  on  the  outer  slope  of  the  dam. 
Any  clay,  sand  or  other  materials  of  good  quality  should  be  similarly 
disposed  of  to  be  utilized  later  by  being  incorporated  in  the  body  of 
the  structure. 

Placing  of  Materials  in  the  Dam. — There  are  in  use  many  different 
methods  of  placing  materials  in  the  dam,  namely,  by  teams  and 
scrapers,  by  wagons  hauled  by  horses  or  traction  engines,  by  railroad 
cars,  by  cableways,  by  mechanical  conveyors  or  by  the  action  of 
water  itself  in  the  hydraulic  processes.  Selection  of  the  particular 
method  to  be  used  is  dependent  upon  the  size  of  the  structure,  the 
location  of  the  materials  to  be  moved,  and  other  conditions.  For  a 
small  dam  it  may  be  impracticable  to  provide  an  expensive  system 
of  traction,  while  for  a  large  structure  an  elaborate  preliminary 
equipment  may  result  in  the  greatest  final  economy. 

The  simplest  method  of  loosening  and  moving  dirt  and  one 
which  is  generally  used  in  the  construction  of  small  earth  dams  is 
by  plow  and  drag,  slip  or  wheel  scraper.  Suitable  material  found 
in  the  vicinity,  is  loosened  by  blasting  if  necessary,  plowed  up  and 
then  hauled  into  place  by  the  scrapers.  Skill  and  care  are  necessary 
in  depositing  the  material  in  such  way  that  it  will  be  thoroughly 
trampled  by  the  horses.  It  should  be  kept  sufficiently  moist  to 
compact  readily,  and  if  not  well  trampled  by  the  men  and  horses, 
the  earth  should  be  further  compacted  by  systematic  rolling. 

In  depositing  the  earth  or  other  material,  it  should  be  spread  out 
in  thin  layers  and  not  allowed  to  accumulate  in  small  piles.  These 
layers  should  average  not  more  than  6  to  8  in.  in  thickness  and  be 


PLATE  XIII 


FIG.  A. — Foundations  for  earth  dam,  showing  excavation  for  puddled  core  and 
earth  being  brought  to  the  site  by  railroad  train,  then  distributed  and  rolled  in 
thin  layers.  Umatilla  Project,  Ore. 


FIG.  B. — Earth  dam  partly  protected  by  heavy  gravel  on  water  side.     Boise 

Project,  Idaho. 

(Facing  Page  214) 


PLATE  XIII 


FIG.  C. — Hydraulic  construction  of  earth  dam,  giant  in  foreground  washing 
earth  and  small  rocks  into  flumes  supported  on  trestles  and  conveying  materials 
to  site  of  dam.  Okanogan  Project,  Wash. 


FIG.  D. — Completed  dam  built  by  hydraulic  process,  shown  above. 


EARTH  DAMS  215 

kept  wetted  by  hose  or  other  means  to  a  degree  sufficient  to  give  the 
most  dense  mass  possible  when  compacted. 

Where  large  quantities  of  material  are  to  be  handled  and  especially 
where  the  borrow  pits  are  located  at  some  considerable  distance 
such  as  half  a  mile  or  more,  it  is  necessary  to  provide  more  economi- 
cal and  quicker  modes  of  conveyance  than  by  horses  and  scrapers 
or  carts.  In  such  cases,  small  construction  railroads  are  generally 
used  and  trains  of  from  five  to  ten  cars,  each  holding  from  2  to  3 
yd.  of  earth  or  more,  are  employed.  (See  Plate  XIII,  Fig.  A.)  The 
earth  is  usually  excavated  by  steam  shovel  or  similar  device,  and  the 
cars  carry  it  upon  the  embankment  or  upon  a  trestle  adjacent  to  it. 
The  economy  of  this  method  of  conveying  earth  is  dependent  largely 
upon  the  arrangement  of  the  tracks,  so  that  the  steam  shovel  and 
trains  will  move  in  unison  and  there  will  always  be  ready  a  train  to 
receive  the  earth  from  the  shovel  and  at  the  same  time  this  train  will 
not  be  delayed  in  getting  its  load.  In  place  of  the  train  it  is  occasion- 
ally economical  to  use  dump  wagons  drawn  by  horses,  these  being 
organized  in  a  way  similar  to  that  in  the  handling  of  trains,  the 
wagons  following  a  certain  route,  so  as  to  come  under  the  shovel  at 
proper  intervals  without  delay. 

The  earth  dumped  from  the  side  of  the  trains  or  wagons  must  be 
spread  and  rolled  by  some  suitable  means.  This  spreading  and 
compacting  is  usually  accomplished  by  drag  scrapers  and  by  horse 
or  steam  roller,  or  similar  device.  In  arranging  the  trestles  for 
delivering  the  earth  by  train  at  the  site  of  the  dam,  they  should  be 
so  planned  as  not  to  come  within  the  structure  itself.  In  a  few 
instances,  large  earth  dams  have  been  built  by  simply  side  dumping 
from  parallel  trestles,  as  is  occasionally  done  in  building  large  railroad 
fills.  This  leaves  the  timbers  embedded  in  the  body  of  the  embank- 
ment which  is  allowable  in  a  railroad  fill  or  to  a  small  extent  in  an 
earth  dam  yet  the  decaying  wood  may  become  a  source  of  danger. 
The  embedded  timbers  if  large  in  aggregate  bulk  prevent  the  earth 
from  settling  uniformly  and  there  are  apt  to  be  spaces  along  the 
timbers  where  the  water  can  find  its  way  and  as  these  rot  away  the 
settling  becomes  unequal  and  there  is  liability  of  leakage  or  failure 
of  the  dam. 

Placing  of  Materials  by  Hydraulic  Method. — The  building  of  a 
dam  of  earth  and  small  rock  by  hydraulic  methods  consists  essentially 
of  the  process  of  dislodging  the  material  by  means  of  a  stream  of 
water  undercutting  and  washing  it  down,  collecting  the  mud-laden 
stream  in  suitable  flumes  and  keeping  this  stream  moving  at  rela- 


216      PRINCIPLES  OF  IRRIGATION  ENGINEERING 

tively  high  velocity  so  that  it  will  not  deposit  the  material  which  'it 
is  carrying  until  the  point  is  reached  where  it  is  desired  to  leave  it. 

In  order  that  this  process  of  moving  and  depositing  earth  may  be 
economically  carried  on,  it  is  necessary  to  have,  first,  a  small  con- 
tinuous flow  of  water  under  sufficient  head,  say  100  ft.  or  more,  so 
as  to  have  under  control  a  powerful  stream  which  can  be  directed 
against  the  unconsolidated  materials,  such  as  clay,  sand  and  gravel, 
to  be  moved;  second,  these  materials  for  economical  construction 
should  be  at  an  elevation  sufficiently  above  the  location  of  the 
proposed  dam  so  that  the  muddy  water  will  flow  by  gravity  to  the 
point  where  the  materials  are  to  be  deposited  although  they  may  be 
lifted  by  centrifugal  pumps;  third,  the  earth  or  small  rock  in  the  bank 
or  pits  to  be  used  must  be  composed  cf  large  and  small  particles, 
such  that  when  placed  these  may  be  mingled  to  form  an  impervious 
mass  or  core  within  the  body  of  the  dam.  If  these  and  other  less 
essential  conditions  are  easily  fulfilled  it  may  be  practicable  to  move 
the  material  into  place  at  a  cost  far  less  than  by  other  means. 

This  process  of  hydraulic  sluicing  is  an  outgrowth  of  the  experience 
of  the  hydraulic  miners  of  California  in  washing  gold-bearing  gravels 
from  ancient  river  beds.  The  water  for  washing  is  collected  in  small 
mountain  reservoirs  or  conducted  from  a  perennial  mountain  stream 
by  flumes  or  small  canals  to  a  point  as  near  as  possible  above  the 
bank  to  be  washed.  Here  it  is  turned  into  a  pipe  or  penstock  which 
terminates  in  a  flexible  hose  with  nozzles  designed  to  give  a  high 
velocity  to  the  stream.  The  arrangement  of  the  nozzles  and  acces- 
sory parts  for  controlling  it  is  known  as  a  hydraulic  giant.  The 
giant  is  so  mounted  that  it  can  be  handled  by  one  or  twc  men,  the 
stream  being  allowed  to  play  against  the  bank  and  moved  up  and 
down  or  swung  from  side  to  side  in  accordance  with  the  judgment  of 
the  operator. 

The  water  striking  the  bank  tears  out  the  lighter  portions  and 
undermines  the  more  solid  parts.  It  carries  in  suspension  the 
smaller  particles  and  rolls  along  stones  up  to  a  weight  of  TOO  lb.,  or 
even  more.  As  soon  as  possible  after  leaving  the  foot  of  the  bank 
the  stream  is  conducted  into  wooden  flumes,  the  process  being 
assisted  by  one  or  more  men  using  long-handled  shovels  or  forks  to 
keep  the  water  and  stones  moving  along  and  remove  obstacles  which 
collect  in  the  stream,  as  shown  on  Plate  XIII,  Fig.  C. 

The  slope  of  the  flumes  must  be  carefully  adjusted  to  maintain  a 
velocity  sufficient  to  keep  the  material  from  being  deposited.  They 
are  continued  on  trestles  out  to  the  site  of  the  dam  and  branches 


EARTH  DAMS 


217 


are  provided  commanding  the  entire  foundation.  Gates  or  openings 
in  the  sides  of  these  flumes  are  provided  at  the  necessary  points  for 
discharging  the  water  near  the  upper  and  lower  faces  where  the 
larger  stones  are  needed.  From  these  points  the  smaller  stones  and 
fine  material  are  carried  inward  toward  the  center  of  the  dam. 
Along  the  axis  of  the  dam  the  muddy  water  is  held  temporarily  in  a 
small  pond  in  which  the  finer  sediment  is  deposited  thus  forming 
a  water-tight  core. 


llwaj  Channel 
(Concrete  lined) 

Scale  of  Feet 
p       so     100     ISP 


o     Drill  Holes 

o    Test  Pits 

A    Points  of  Control 
~*~  Rock  Outcrop 
••  +  +  Vitrified  Drain  Pipe 

(Item  10  Schedule  1) 
///////,  Concrete  Slope 


FIG.  42. — General  plan  of  Conconully  Dam,  showing  location  of  spillway  and 
outlet  works,  Okanogan  Project,  Washington. 

As  a  result  of  careful  manipulation  of  the  flumes  the  large  rocks 
are  deposited  on  the  outside  of  the  dam,  the  smaller  stones  and 
gravel  inside  of  this  and  the  finest  sand  and  silt  in  the  center  or  near 
the  up-stream  face.  To  bring  about  this  result  the  flumes  are  shifted 
inward  on  the  dam  as  the  structure  increases  in  height;  finally  a 
single  flume  deposits  the  last  of  the  material  on  the  crest,  resulting 


218      PRINCIPLES  OF  IRRIGATION  ENGINEERING 

in  a  symmetrical  structure  as  shown  on  Plate  XIII,  Fig.  D.  The 
general  plan  of  the  particular  work  shown  in  this  plate  is  given  in 
Fig.  42,  this  being  the  Conconully  dam  across  Salmon  River  furnish- 
ing water  for  the  Okanogan  Project,  Wash.  The  area  from  which 
the  material  has  been  taken  by  sluicing  is  shown  on  the  hillside  in 
the  lower  part  of  the  drawing,  being  nearly  adjacent  to  the  site  of 
the  dam. 

Among  the  objections  to  the  hydraulic  method  of  constructing 
earth  dams  are  those  which  arise  from  the  limitations  imposed  by 
the  quantity  of  water  available  for  sluicing  the  material,  and  the 
difficulty  of  elevating  this  or  bringing  it  to  the  required  height 
above  the  dam  to  be  built.  In  other  words,  there  is  usually  not 
sufficient  elasticity  in  the  limiting  condition  to  meet  all  of  the 
requirements,  for  example,  it  may  be  discovered  after  the  work  is 
well  opened  up,  that  the  best  material  to  be  utilized  for  the  dam  is 
located  a  little  too  low  to  be  effectively  washed  or  the  position  of 
attack  must  be  changed,  necessitating  a  reconstruction  of  the 
conveying  flume. 

A  more  serious  objection  is  that  arising  from  the  tendency  of 
material  handled  in  this  way  to  be  sorted  or  stratified,  for  example, 
if  the  work  is  not  carefully  managed,  it  may  happen  that  for  a  brief 
period  sand  may  be  washed  into  the  dam  and,  due  to  the  action  of 
the  water,  deposited  as  a  thin  layer.  The  finer  particles  or  mud  will 
not  penetrate  this  layer  of  sand  and  thus  there  is  formed  a  line  of 
stratification  or  thin  layers  of  different  degrees  of  fineness,  offering 
opportunity  for  percolation  or  for  sliding  of  one  portion  of  the  dam. 
Another  objection  lies  in  the  fact  that  if  there  is  an  undue  proportion 
of  fine  clay  in  the  center  of  the  dam,  this  will  not  deliver  its  excess 
water,  except  with  great  slowness,  and  remains  a  mass  of  unconsoli- 
dated  material  liable  to  behave  as  a  semi-fluid. 

The  principal  benefit  claimed  for  this  method  is  the  relatively 
low  cost  of  moving  the  material.  When  the  conditions  are  favorable, 
it  is  remarkably  cheap,  far  less  than  the  ordinary  procedure  by  means 
of  plow,  scraper,  or  hauling,  but,  as  before  stated,  does  not  have  the 
adaptability  of  the  latter.  Some  extraordinarily  low  figures  have 
been  given  of  the  actual  cost  of  less  than  5  cents  per  yard,  but  this  is 
where  great  quantities  have  been  moved  with  a  very  conveniently 
located  bank  of  earth  and  with  ample  water  supply.  Under  ordinary 
conditions  the  cost  is  higher  and  for  most  localities  the  conditions 
are  so  unfavorable  that  the  cost  is  prohibitive. 

Compacting  the  Material. — The  proper  compacting  of  the  material 


EARTH  DAMS  219 

in  an  earth  dam  is  one  of  the  most  important  details  of  construction. 
It  may  be  done  by  simple  or  crude  means.  On  smaller  earth  dams 
built  by  hand  labor  or  by  plow  and  scraper  the  earth  can  usually  be 
compacted  sufficiently  by  the  trampling  of  men  and  animals.  In 
some  cases,  the  dam  has  been  enclosed  with  a  suitable  fence  and 
animals,  bands  of  sheep,  goats,  range  cattle,  or  horses  have  been 
driven  backward  and  forward  over  the  area. 

A  more  systematic  procedure  is  to  utilize  a  roller  drawn  by  horses 
or  driven  by  steam  or  gasoline  engine.  The  surface  of  the  roller  is 
usually  corrugated,  or  the  roller  may  be  made  of  rings  moving 
loosely  upon  an  axle,  so  that  each  ring  acts  as  an  independent  wheel, 
settling  into  the  inequalities  of  the  surface.  A  smooth  roller  is 
objectionable  as  tending  tc  form  distinct  planes  through  which  water 
may  seep.  While  the  surface  is  being  compacted  it  should  be  kept 
moist. 

Ramming  by  hand  or  by  machinery  is  sometimes  practised, 
especially  over  small  areas,  particularly  where  a  closure  cf  an  earth 
dam  is  being  made  in  a  gap  in  the  structure.  Here,  especial  atten- 
tion must  be  given  to  thoroughly  compacting  the  earth  and  to  the 
details  of  forming  a  close  bond  with  the  adjacent  slopes.  Light 
steam  hammers  have  been  utilized  for  rapid  work  in  such  confined 
spaces  to  secure  quick  results. 

Prevention  of  Seepage  through  the  Dam. — The  making  of  an 
impervious  wall  or  layer  in  an  earth  dam  is  a  prime  requisite.  It  is 
relatively  easy  to  put  enough  material  in  place  to  hold  back  the 
water  and  to  prevent  the  structure  being  washed  away,  but  it  is  far 
more  difficult  to  arrange  this  material  so  that  water  cannot  find  its 
way  through  minute  channels  or  along  contact  planes.  Primarily, 
seepage  is  prevented  by  a  proper  selection  and  mixing  of  materials 
and  by  compacting  them  thoroughly  when  deposited.  There  are, 
however,  a  number  of  devices  for  securing  impermeability,  each  of 
these  being  used  to  greater  or  less  extent,  in  accordance  with  the  sur- 
rounding conditions  and  especially  the  character  of  material  available. 
They  may  be  classified  as  (a)  core  walls,  (b)  puddled  core,  and 
(c)  water-tight  face. 

Core  Wall. — A  core  wall  consists  of  a  concrete,  masonry,  timber, 
or  metal  wall  or  diaphram  built  within  the  dam  usually  near  its 
center  or  toward  the  upper  face  and  made  as  nearly  impervious  as 
possible.  (See  Plate  XIV,  Fig.  A.)  It  is  usually  thin  (Fig.  43) 
and  is  held  in  place  by  the  adjacent  mass  of  earth  and  rock.  If 
built  of  concrete  or  masonry  it  is  founded,  if  possible,  upon  solid 


220     PRINCIPLES  OF  IRRIGATION  ENGINEERING 


rock;  where  rock  is  some  dis- 
tance below  the  surface  a  nar- 
row trench  is  excavated  to  it 
along  the  axis  of  the  dam. 
This  trench  is  then  filled  with 
the  masonry  or  concrete.  If 
it  is  impracticable  to  reach 
bedrock  by  digging  the  core  wall 
may  be  founded  upon  steel  or 
wooden  sheet  piling  driven 
sufficiently  deep  to  penetrate 
to  an  impervious  stratum. 

Instead  of  the  concrete  core 
wall,  the  sheet  piling  may  be 
continued  longitudinally  up 
through  the  dam  by  a  stout 
wooden  or  plank  fence  or  bulk- 
head made  water  tight  by 
sheathing  or  by  plates  of  metal 
suitably  joined  or  riveted  to- 
gether. These  extend  through 
the  dam  longitudinally  from 
side  to  side  of  the  valley.  An 
objection  to  the  use  of  a 
metal  or  wood  cut-off  wall  or 
diaphragm  in  this  connection 
is  the  liability  to  deterioration 
through  the  rotting  or  rusting 
of  the  material. 

All  core  walls  are  subject  to 
the  further  objection  that  the 
earth  or  main  body  of  the  dam 
in  the  course  of  settlement  may 
shrink  or  pull  away  or  that  the 
wall  may  be  ruptured  by  an 
equal  settlement  thus  leaving 
plane  of  weakness  or  cracks 
through  which  water  may 
percolate.  It  is  very  difficult, 
if  not  impossible,  to  make  a 
good  bond  or  tight  joint  between 


EARTH  DAMS 


221 


the  core  and  the  material  composing  the  main  body  of  the  dam. 
It  is  held  by  some  engineers  that  a  thin  core  wall  or  diaphragm 
should  not  be  relied  upon  to  produce  water-tightness  in  an 
earthen  dam,  but  that  it  serves  a  useful  purpose  in  preventing 
animals  burrowing  through  the  embankment.  Nevertheless,  it 
is  believed  there  are  some  conditions  where  the  building  of 
a  thin  core  wall,  especially  of  concrete  and  the  holding  of  this 
in  place  by  earth  and  rock  afford  a  satisfactory  and  econom- 
ical method  of  construction.  Such  conditions  have  been  met  at  the 
earth  dam  closing  the  outlet  of  Strawberry  Valley  in  Utah,  the 
section  of  the  dam  being  given  in  Fig.  44. 


JUN 

H_80 

HIO    Toe  Trench  \        Solid  Blue  Limestone  with  Seams 
Cut-oST  Trench  to  Rock 


Core  \Yall  to  Solid  Rock 


FIG.  44. — Section  of  earth  dam  with  concrete  core  wall  and  cut-off  trenches, 
Strawberry  River,  Utah. 

Puddle  Core. — Instead  of  attempting  to  make  a  tight  wall  or 
diaphragm  within  the  dam,  it  is  practicable  in  most  cases  to  secure 
as  good,  or  better,  results  by  careful  selection  of  fine  earth  or  clay, 
mixing  this  in  proper  amounts  so  as  to  secure  a  compact  mud  or 
puddle  impervious  to  water.  Skill  and  judgment  must  be  employed 
in  selecting,  mixing,  and  placing  the  puddle,  but  if  well  done  the 
resulting  condition  may  be  preferable  to  the  building  of  a  concrete 
or  other  core,  because  of  the  fact  that  the  mass  of  the  dam  is  more 
nearly  homogenous  and  settlement  occurs  without  disrupting  or  the 
opening  of  the  joints  or  planes  of  seepage.  An  objection,  however, 
to  the  puddle  core  is  that  it  may  be  penetrated  by  burrowing  animals, 
and  if  once  punctured  is  eroded  by  the  percolating  waters. 

Water-tight  Face. — An  impervious  layer  may  under  some  condi- 
tions be  placed  on  the  upper  or  water  face  of  the  dam  to  advantage. 
This  form  of  construction  in  many  ways  is  more  logical  and  conforms 


222      PRINCIPLES  OF  IRRIGATION  ENGINEERING 

more  to  the  theory  of  a  dam,  namely,  of  a  water-tight  wall  or  layer 
held  in  place  by  sufficient  material  to  prevent  its  being  broken  or 
swept  away.  When  this  water-tight  layer  is  put  in  the  center  as  a 
core  wall  it  cannot  be  inspected,  but  if  placed  on  the  upper  surface 
it  can  be  examined  or  repaired  whenever  water  is  drawn  from  the 
reservoir.  A  water-tight  face  is,  however,  difficult  and  expensive 
to  construct  and  maintain. 

To  make  this  water-tight  face,  the  simplest  method  employed  in 
small  dams  is  by  the  use  of  inclined  wooden  covering  or  sheathing. 
Planks  are  held  in  place  by  suitable  means  and  the  joints  closed  by 
battons  or  are  caulked  to  form  as  nearly  a  water-tight  surface  as 
possible.  In  some  instances  sheets  of  iron  or  steel  have  been  thus 
used,  being  provided  with  expansion  joints  and  carefully  protected 
from  rusting  by  paint  or  various  mixtures.  Such  metal  covering  is 
held  in  place  by  steel  beams,  or  by  a  backing  of  concrete  or  similar 
material,  and  may  be  covered  by  a  thin  layer  of  concrete.  The  use 
of  wood  or  steel  may  be  considered  as  more  or  less  of  a  temporary 
expedient,  as  the  wood  must  be  frequently  renewed,  owing  to  rapid 
decay  due  to  the  rise  and  fall  of  the  water  and  alternate  exposure  to 
the  waves  and  to  the  wind.  The  metal  also  corrodes,  especially 
at  the  joints  where  it  is  not  always  easy  to  secure  perfect  covering. 

Cement  or  asphalt  or  a  combination  of  both  are  occasionally  used 
for  this  water-tight  layer,  especially  in  small  reservoirs  for  city 
supply.  The  expense  is  prohibitory  for  larger  works  needed  for 
irrigation. 

Care  must  be  taken  to  provide  adequate  drainage  for  water  which 
may  percolate  into  the  center  of  the  dam  through  these  wooden, 
metal  or  other  coverings,  and  to  see  to  it  that  the  material  composing 
the  mass  of  the  dam  is  sufficiently  pervious  to  let  this  water  escape 
without  creating  internal  hydraulic  pressure  or  uplift  which  will 
tend  to  reduce  the  weight  of  the  dam  and  permit  it  tc  slide. 

Cut-off  Trenches. — The  cut-off  trenches  are  located  in  the  upper 
portion  and  are  made  continuous  with  the  core  wall  or  less  pervious 
materials  of  the  dam.  Usually  one  cut-cff  trench  is  considered 
sufficient,  but  conditions  may  arise  where  two  or  more  may  be 
desirable.  The  trenches  are  planned  and  excavated  in  accordance 
with  evidence  as  to  the  character  of  the  underlying  material  obtained 
by  the  test  pits  or  drilled  holes.  They  are  usually  as  narrow  as  can 
be  conveniently  made  and  may  be  extended  to  an  almost  indefinite 
depth,  if  upon  opening  up  the  material  is  found  to  be  notably 
pervious  to  water.  In  some  cases,  under  earth  dams,  they  have  been 


EARTH  DAMS  223 

carried  down  to  a  depth  of  nearly  100  ft.  and  then  further  extended, 
as  before  stated,  by  driving  sheet  piling  at  the  bottom. 

In  refilling  the  cut-off  trenches  great  care  must  be  exercised  in 
selecting  the  material  and  in  packing  it  in  place.  Sufficient  sand 
or  gravel  should  be  included  with  the  fine  clay  or  other  available 
materials,  to  make  a  firm  mixture,  and  one  in  which  the  voids  will  be 
filled  as  nearly  as  possible.  The  resulting  mass  should  be  moistened 
and  tamped  until  thoroughly  compacted. 

In  some  cases,  especially  when  the  cut-off  trench  is  carried  to 
rock,  it  is  desirable  to  build  in  it  a  thin  wall  of  concrete.  If  the 
trench  is  very  narrow  and  the  walls  of  the  excavation  will  stand 
sufficiently  long,  it  can  be  filled  with  concrete  and  the  trench  thus 
used  in  place  of  wooden  or  other  forms  for  holding  the  concrete  in 
place  during  the  time  of  setting. 

Protection  of  Slopes. — The  slopes  of  the  dam  must  be  protected 
from  the  erosive  activities  of  the  rain  and  wind.  Any  uncovered 
bank  of  earth  is  quickly  carved  and  corrugated  unless  well  protected. 
Such  protection  is  afforded  either  by  a  pavement  of  stone  or  by  a 
growth  of  grass  or  plants  whose  roots  hold  the  earth  in  place. 

On  the  water  side  the  protection  must  be  of  the  firmest  possible 
nature,  owing  to  the  constant  attack  of  the  waves.  As  the  water 
rises  and  falls  in  the  reservoir  and  especially  at  points  where  exposed 
to  the  wind,  the  waves  cut  beaches  or  terraces  and  tend  to  leave  the 
banks  of  the  reservoir  in  a  series  of  horizontal  lines.  On  the  outside 
or  land  side,  the  erosion  due  to  the  weather  generally  takes  the  form 
of  nearly  vertical  lines  and  here  the  less  expensive  covering  may  be 
provided  of  turf  or  grass. 

For  the  water  slope,  heavy  stone  or  riprap  is  required.  This 
should  be  so  placed  that  the  stones  interlock,  and  that  the  sweep  of 
the  waves  will  not  dislodge  them.  The  foot  of  the  slope  must  be 
carefully  arranged  to  sustain  the  weight  or  resist  any  tendency  to 
slide.  The  angle  of  the  slope  should  be  sufficiently  flat  so  that  the 
stone  pavement  will  rest  upon  it.  This  angle  is  dependent  upon 
the  character  of  the  underlying  material.  In  the  case  of  clay  not 
well  drained,  the  water  penetrating  beneath  the  pavement  on  even 
a  relatively  flat  slope  may  cause  the  sloughing  of  the  bank,  carrying 
with  it  the  stone  pavement.  (See  Plate  XIV,  Figs.  C  and  D.) 

On  the  dry  side  also,  the  character  of  covering  is  dependent 
largely  upon  the  material  in  the  bank  and  plants  and  grasses  selected 
must  be  with  reference  to  the  angle  of  slope  and  constituent  material. 


224      PRINCIPLES  OF  IRRIGATION  ENGINEERING 

Drainage  of  Dam. — One  of  the  elements  of  safety  of  an  earthen 
structure  is  in  preventing  saturation  especially  on  the  lower  or  land 
side  of  the  impervious  layer  or  puddle  core.  It  is  assumed  that  the 
dam  may  be  saturated  to  this  diaphram  or  core  and  that  a  small 
amount  of  water  will  penetrate  through  it.  This  water  and  that 
which  falls  in  rain  upon  the  surface  must  be  quickly  conducted  away 
so  as  to  leave  the  lower  side  relatively  dry  and  thus  prevent  the 
tendency  to  slipping  or  sliding  resulting  from  the  presence  of  wet  or 
soggy  material.  In  preparing  foundations  of  the  dam,  drains  must 
be  arranged  and  tile  of  suitable  size  placed  longitudinally  to  the  dam 
in  such  a  way  as  to  catch  and  carry  out  to  the  lower  toe  any  water 
which  may  be  percolating  through  the  puddle  core.  At  different 
heights  in  the  dam  also  other  drains  should  in  some  cases  be  con- 
structed for  carrying  the  water  out  to  the  lower  slope  where  it  can 
be  caught  in  suitable  gutters. 

Dikes. — The  term  dike  is  applied  to  low,  long  earth  dams,  usually 
built  parallel  to  the  general  course  of  a  river  or  along  the  shore  of  a 
body  of  water  to  prevent  the  land  from  being  overflowed  by  floods 
in  the  river  or  by  high  tides  or  similar  fluctuations  in  height  of  water. 


Rolled 
Embankment 

8"Layers 
Original  Surface 


w 


•          FIG.  45. — Cross-section  of  earth  dike  with  pavement  on  water  side. 

The  term  dike  is  also  applied  to  a  long,  relatively  low  extension  of 
an  earth  dam  where  the  topography  of  the  country  is  such  that  the 
dam  must  be  continued  for  some  distance  across  low  grounds.  It 
frequently  happens  that  in  the  prolongation  of  an  earth  dam  the 
topography  is  such  that  rising  ground  cuts  out  the  necessity  of  the 
dam  or  dike  for  a  space  of  a  few  hundred  or  thousand  feet  and  then 
a  depression  occurs  which  must  be  closed  by  a  low  structure  which 
may  be  considered  as  a  continuation  of  the  main  dam,  in  which 
case  the  term  dike  is  often  used  for  each  of  these  smaller  earth 
dams. 

The  principles  of  construction  of  dikes  of  this  character  is  prac- 
tically the  same  as  those  discussed  for  earth  dams  in  general.     One 


PLATE  XIV 


FIG.  A. — Concrete  core  wall  in  earth  dam.     Carlsbad  Project,  N.  Mex. 


FIG.  B. — Loose  rock  protection  of  earth  dam  on  water  side. 
Project,  Ore. 


Umatilla 


(Facing  Page  224.) 


PLATE  XIV 


FIG.  C. — Paving  on  water  side  of  earth  embankment.     Belle  Fourche  River, 

So.  Dak. 


FIG.  D. — Concrete  block  protection  against  wave  action  on  earth  dam.     Belle 
Fourche  Project,  So.  Dak. 


EARTH  DAMS  225 

or  more  cut-off  trenches  are  provided  and  the  water  slopes  paved, 
as  indicated  in  Figs.  43  and  45  and  on  Plate  XIV,  Fig.  B. 

Limits  of  Height  of  Earth  Dams. — A  few  earth  dams  have  been 
built  to  a  height  of  over  100  ft.,  but  the  majority  of  structures  of 
unconsolidated  materials  do  not  exceed  from  50  to  70  ft.  in  height. 
If  carefully  built,  there  is  no  reason  for  limiting  the  height,  as  it  is 
conceivable  that  earth  may  be  so  selected,  arranged,  and  piled  up 
in  such  massive  form  as  to  form  practically  a  range  of  hills  or  a 
barrier  comparable  to  that  built  by  nature.  The  mechanical  or 
engineering  difficulties  are  not  great,  but  the  limit  to  be  placed  is 
that  of  cost,  since  the  width  or  base  of  any  high  structure,  especi- 
ally one  of  earth  must  be  correspondingly  great.  The  cost  therefore 
increases  rapidly  with  the  height  due  to  extra  material  which  must 
be  selected  and  handled  and  the  greater  care  required  to  prevent 
defects  in  the  work. 

Examples  of  Earth  Dams. — Of  the  higher  earth  dams  some  of  the 
more  noteworthy  are  those  recently  built  by  the  Reclamation 
Service,  the  highest  being  that  on  the  Belle  Fourche  project  in  South 
Dakota,  across  Owl  Creek,  115  ft.  in  height,  and  6,200  ft.  long, 
containing  i  ,600,000  cu.  yd.  Also  the  dam  on  the  Umatilla  project 
in  Oregon,  known  as  the  Cold  Springs  Dam,  98  ft  high  and  3,800  ft. 
long,  containing  757,000  cu.  yd.  of  earth  and  gravel  and  32,500  cu. 
yd.,  of  rock  fill.  For  comparison  with  these  may  be  cited  the 
Tabeaud  Dam  in  California,  123  ft.  high,  635  ft.  long  and  containing 
37°>35°  cu-  yd-,  also  the  San  Leandro  Dam  in  California,  125  ft. 
high,  500  ft.  long,  and  containing  542,700  cu.  yd. 


15 


CHAPTER  XV 
ROCK-FILL  DAMS 

Description. — A  rock-fill  dam  consists  essentially  of  a  barrier  or 
embankment  of  loose  rock  with  its  up-stream  face  covered  with  an 
impervious  layer  or  blanket.  It  is  the  function  of  the  rock  portion 
of  the  structure  to  resist  the  pressuie  of  the  water  and  hold  in  posi- 
tion, against  this  pressure,  the  water-tight  face,  which  in  reality 
forms  the  dam. 

The  rock  section  of  the  dam  may  consist  of  large  and  small  stones 
dropped  or  dumped  into  place  with  little  or  no  attempt  at  systematic 
arrangement,  each  stone  being  allowed  to  take  its  own  position. 
The  width  of  base  of  the  rock  barrier  is  sufficient  so  that  the  weight 
of  the  stones  and  the  friction  between  them  prevents  any  tendency 
of  the  structure  to  overturn,  or  its  parts  to  slide  on  each  other.  As 


Hijrh  Water 
Bpillw«j  Crest 


^  Ground  Surface i  ^/Approiimat«_Rocl^Burfmc« 


SO  Trench  to  be  Dug   to 
Bock  and  Refilled       ' 

(See  Specifications  Par.    )     Typical  Section  of  Earth  and  Rock-Fill  Dam 


FIG.  46. — Typical  section  of  earth  and  rock-fill  dam,  Clear  Lake  dam, 
Klamath  Project,  Oregon. 

compared  to  an  earth  dam,  each  component  part  or  stone  is  relatively 
large  and  heavy.  It  is,  therefore,  held  in  place  by  its  weight  and 
also  by  the  rough  or  angular  projection  of  its  neighbors. 

The  water-tight  portion  or  face  of  the  dam  may  be  of  various 
materials,  such  for  example,  as  wood,  steel,  concrete  or  earth.  The 
more  common  of  these,  especially  for  dams  constructed  during  the 
past  few  years,  is  earth.  The  thickness  of  this  earth  covering 
is  made  to  vary  slightly,  due  to  the  character  of  materials  available 
and  other  local  conditions.  Its  thickness  also  increases  from  the 
top  to  the  base  of  the  dam  as  shown  in  Fig.  46.  For  high  dams  the 

226 


ROCK-FILL  DAMS  227 

earth  thus  forms  a  considerable  portion  of  the  total  materials  re- 
quired. Dams  built  in  this  manner,  partly  of  rock  and  partly  of 
earth  are  commonly  designated  as  rock-  and  earth-fill  dams. 

Advantages  over  Earth  Dams. — The  principal  advantage  of  rock- 
fill  over  earth  dams  is  that  the  former  is  less  likely  to  be  injured  or 
washed  away  by  overtopping  during  extraordinary  floods  or  unex- 
pected occurrences.  There  is  also  some  advantage  in  the  methods  of 
construction  which  may  be  employed,  -due  to  the  fact  that  a  limited 
quantity  of  water  can  be  passed  through  the  rock  portion  of  the  dam 
without  serious  injury. 

If  water  rises  in  an  ordinary  earth  dam,  and  finds  a  channel  over 
or  through  it,  the  structure  is  doomed,  as  the  component  particles  are 
too  small  to  resist  erosion.  Such  a  failure  may  be  rapid,  due  to  the 
ease  with  which  the  earth  is  eroded  and  the  flood  thus  let  loose  causes 
great  damage.  A  rock-fill  dam  on  the  other  hand  may  pass  a  con- 
siderable quantity  of  water  over  or  through  it  without  being  washed 
away,  or  even  seriously  damaged.  Even  though  the  earth  portion  of 
the  structure  should  be  eroded  and  carried  away  through  the  loose 
rock,  there  is  a  probability  of  the  latter  holding  and  reducing  in  a 
great  degree  the  magnitude  of  the  flood. 

In  constructing  a  rock-fill  dam,  especially  on  a  periodic  stream,  it  is 
frequently  an  advantage  to  deposit  the  rock,  or  a  portion  of  it,  in 
running  water,  the  earth  or  water-tight  portion  being  built  during 
the  low  water  or  dry  stage  of  the  stream.  The  rock  in  this  case  is 
dropped  into  the  stream  and  partly  washed  into  place,  the  slopes 
adjusting  themselves  while  the  water  is  flowing  over  or  through  the 
mass.  This  results  in  some  waste  of  material,  as  there  is  a  tendency 
for  the  rock  to  be  washed  do  wn-stream  below  the  assumed  toe  of  the 
structure.  Where  plenty  of  material  is  at  hand  and  cheaply  moved, 
this  may  be  no  serious  disadvantage.  It  is  also  possible  to  construct 
the  water-tight  portion  of  the  dam  in  a  stream  of  moderate  size,  by 
first  covering  the  upper  face  of  the  loose  rock  with  small  stones  which 
will  be  washed  into  the  larger  openings  and  then  adding  on  top  of  this 
successive  layers  of  gravel,  sand  and  finally  clay  or  other  fine-grained 
material,  thus  forming  an  impervious  blanket.  This  method  of  con- 
struction also  results  in  loss  of  earth,  as  some  of  the  fine  grains 
are  carried  into  or  through  the  loose  rock.  Material,  both  earth  and 
rock,  if  deposited  in  water  are  as  a  rule  more  firmly  compacted  and 
less  liable  to  settlement  than  if  built  up  dry. 

Site  to  Which  Adapted. — Almost  any  site  suitable  for  an  earth 
dam  is  equally  well  adapted  to  one  of  the  rock-fill  type,  provided  the 


228      PRINCIPLES  OF  IRRIGATION  ENGINEERING 

necessary  materials  for  its  construction  are  at  hand.  The  most 
favorable  site  is  one  with  sufficient  quantities  of  rock  situated  near  it 
and  at  sufficient  elevation  so  that  it  can  be  shot  down  and  easily 
dumped  into  position.  A  soft  bottom  under  the  rock  portion  is  not 
always  an  objection,  especially  if  the  rock  is  placed  in  running  water. 
If  the  bed  is  soft,  the  larger  rocks  sink  rapidly  into  it,  the  stream 
scours  out  the  lighter  material  and  the  mass  is  worked  by  the  water 
well  into  the  foundation  until  securely  held. 

Foundation. — The  remarks  heretofore  made  relative  to  water- 
tightness  of  the  foundation  for  an  earth  dam  apply  equally  for  a 
rock-fill  one.  The  methods  employed  for  preventing  seepage  under 
the  dam  apply  also  in  one  case  as  in  the  other.  That  is  to  say, 
a  constituent  part  of  the  dam,  such  for  example,  as  a  curtain  wall  or 
a  trench  filled  with  water-tight  material  should  be  carried  down  to  an 
impervious  stratum  such  as  rock  or  clay. 

Wherever  a  rock-fill  dam  can  be  built  in  the  dry,  that  is,  where 
the  foundation  can  be  kept  free  from  water  during  construction, 
the  site  to  be  occupied  by  the  dam  should  be  prepared  by  removing 
the  lighter  material.  If  a  solid  bottom  can  be  reached,  special 
attention  should  be  given  to  the  water  or  upper  side  of  the  dam. 
Here  a  cut-off  trench  should  be  put  down  or  sheet  piling  driven 
if  the  underlying  material  is  sufficiently  permeable,  the  object 
being  to  provide  a  continuous  diaphragm  or  sheet  of  impervious 
material  extending  from  bedrock  or  from  a  heavy  bed  of  clay  upward 
into  the  impervious  covering  on  the  upper  face  of  the  dam.  Behind 
or  below  this  covering  or  blanket  the  stone  should  be  arranged 
to  form  as  compact  a  mass  as  possible,  filling  in  the  interstices 
b.etween  the  larger  blocks  with  spawls  and  small  stone  but  leaving 
toward  the  lower  side  of  the  dam  ample  openings  or  drains  for 
taking  away  any  water  which  may  penetrate  to  the  center  of  the  dam. 

Materials. — One  of  the  most  important  questions  for  consideration 
is  that  of  obtaining  economically  a  large  amount  of  heavy  stone 
for  the  body  of  the  dam.  This  can  be  had  usually  from  the  cliffs 
or  rock  exposures  which  are  to  be  found  frequently  on  the  sides  of 
narrow  mountain  valleys  or  gorges,  through  which  a  river  has  cut 
its  way.  By  undermining  these  in  part  or  by  placing  explosives 
in  advantageous  manner,  large  quantities  of  rock  may  be  loosened 
and  thrown  down  in  such  position  that  they  can  be  readily  handled 
and  placed  in  the  dam.  The  small  stones  can  usually  be  had  as  a 
result  of  the  breaking  up  or  moving  of  the  larger  pieces. 

The  size  of  rock  used  may  be  as  large  as  can  be  handled  by  the 


ROCK-FILL  DAMS  229 

facilities  available.  In  order  to  give  stability  to  the  structure, 
the  principal  part  of  the  rock-fill  should  be  composed  of  stones 
weighing  each  a  thousand  pounds  or  more.  The  spaces  between 
these  large  stones  should  be  filled  in  with  smaller  ones.  The  upper 
face  of  the  rock  embankment  should  contain  enough  small  stones 
and  fine  materials  from  the  quarries  to  make  it  sufficiently  tight 
to  hold  the  earth-fill  in  place  and  prevent  its  being  carried  into  the 
rock. 

The  gravel  and  earth  covering,  while  it  may  be  relatively  small 
in  cubical  contents,  frequently  necessitates  relatively  large  expendi- 
tures, as  these  must  be  carefully  selected  and  placed.  Where 
rock  is  abundant  suitable  gravel  and  earth  may  not  be  easily  obtain- 
able but  must  be  brought  from  a  distance.  In  selecting  the  materials 
for  the  earth-fill,  the  same,  or  greater  precautions  for  water  tight- 
ness should  be  taken  as  in  selecting  those  for  an  earth  dam.  When 
a  suitable  mixture  cannot  be  found  in  natural  deposits,  the  materials 
should  be  analyzed  and  properly  combined. 

Section  and  Slopes. — The  most  advantageous  section  for  a 
rock-fill  dam,  like  an  earth  dam,  cannot  be  determined  by  any  known 
mathematical  formulae.  It  is  known  that  dams  of  certain  top  width 
and  slopes  have  stood  successfully,  but  how  much  their  dimensions 
might  be  reduced  and  still  make  a  safe  structure  is  a  question  which 
cannot  be  positively  answered.  The  essential  requirement  is  that 
the  rock-fill  shall  be  heavy  enough  to  prevent  sliding  either  upon 
the  foundation  or  within  the  structure. 

The  slope  of  the  down-stream  face  should  be  sufficiently  flat 
to  prevent  any  tendency  of  the  rock  sliding  upon  it  or  in  other 
words  it  should  be  less  than  the  angle  of  repose  for  the  material 
used.  The  up-stream  face  of  the  rock-fill  should  be  sufficiently 
inclined  to  cause  the  weight  of  the  water-tight  covering  to  be  sup- 
ported largely  upon  it.  This  will  prevent  the  tendency  for  cracks 
being  developed,  due  to  unequal  settlement.  These  conditions 
are  fulfilled  by  a  slope  of  about  i  1/2  to  i  for  the  down-stream  and 
i  or  i  1/4  to  i  for  the  up-stream  face.  Generally  the  up-stream 
slope  of  the  earth  covering  should  not  be  less  than  about  3  to  i. 

The  top  width  of  the  rock-fill  may  vary  from  10  to  20  ft.  and  that 
of  the  earth-fill  from  5  to  10  ft.  depending  upon  the  height  of  struc- 
ture, and  the  distance  below  the  top  of  the  dam  of  maximum  high 
water  in  the  reservoir.  For  very  low  dams  where  flood  condi- 
tions are  not  severe  less  top  widths  than  these  may  be  used  with 
safety. 


230      PRINCIPLES  OF  IRRIGATION  ENGINEERING 

The  up-stream  slope,  if  of  earth,  should  be  protected  from  wave 
action  and  from  sloughing  by  means  of  suitable  paving  or  other 
covering.  The  down-stream  slope  generally  needs  no  protection, 
being  composed  of  heavy  rock.  The  rock  in  this  slope  may  be 
either  hand  placed  or  they  may  be  dumped  roughly  to  the  neat 
lines.  Hand  placing,  while  adding  somewhat  to  the  general 
appearance,  does  not  in  any  other  way  improve  the  work.  In 
fact,  it  is  doubtful  if  a  slope  of  hand-placed  rock  can  be  made  as 
durable  as  one  of  large  stone  dumped  into  position. 

Water-tight  Section. — There  are  various  methods  by  means  of 
which  rock-fill  dams  are  made  water-tight.  Each  of  these  methods 
requires  some  form  of  water-tight  face  or  section  being  placed  on 
the  upper  side  of  the  loose  rock-fill. 

In  the  earliest  examples  of  rock-fill  dams  a  wood  facing  was  com- 
monly used.  It  was  generally  made  of  two  thicknesses  of  matched  or 
tongue  and  grooved  lumber  held  in  place  by  being  spiked  to  a  timber 
framework  which  was  securely  anchored  into  the  rock.  This  form 
of  covering  is  not  entirely  satisfactory  on  account  of  the  rapid  decay 
of  the  timbers  and  also  its  tendency  to  leak  after  a  few  years  service. 
Concrete  facings  have  also  been  used  to  a  limited  extent.  In  these 
there  is  a  tendency  for  the  concrete  to  crack,  due  to  unequal  settle- 
ment in  the  dam.  In  this  connection  it  may  be  well  to  state  that  no 
structure  built  of  unconsolidated  material,  such  as  earth  or  loose 
rock  is  free  from  some  slight  settlement.  This  should  be  taken  into 
account  in  planning  the  work. 

In  the  more  modern  construction  of  rock-fill  dams  a  covering  of 
earth  is  commonly  used  on  the  up-stream  side  of  the  rock-fill.  This 
earth  section  is  some  cases  in  rendered  more  impermeable  by  means 
of  a  puddle  core  of  fine  materials  or  by  a  core  wall  of  concrete  masonry 
as  shown  on  Plate  XV,  Fig.  A.  In  some  instances  walls  made  of 
metal  plates  have  also  been  used  in  the  body  of  the  dams.  Where 
metal  is  used  it  is  coated  with  asphaltum  or  some  similar  rust- 
resisting  substance  and  further  protected  from  injury  and  corrosion 
by  being  backed  with  thin  walls  of  concrete.  One  objection  which 
has  frequently  been  urged  against  the  use  of  thin  walls  in  a  dam  is 
that  they  cannot  be  reached  for  purposes  of  inspection  and  repairs. 

It  is  the  opinion  of  the  writers  where  suitable  puddle  material  is 
available  that  an  earth  section  containing  a  carefully  constructed 
puddle  core  is  the  most  satisfactory  means  of  securing  water-tightness. 
Where  a  core  wall  is  necessary  on  account  of  unsatisfactory  materials 
for  the  earth  section,  one  of  concrete  either  plain  or  with  enough  rein- 


ROCK-FILL  DAMS  231 

forcement  to  prevent  cracking  is  believed  to  be  the  most  satisfactory 
type. 

Seepage  through  a  rock-fill  dam,  on  account  of  its  greater  stability 
and  more  perfect  drainage  in  the  rock  section,  is  not  likely  to  prove  as 
dangerous  as  in  the  ordinary  earth  dam.  Despite  this  fact  however, 
every  reasonable  precaution  should  be  taken  to  reduce  the  seepage  to 
a  minimum. 


CHAPTER  XVI 
MASONRY  DAMS 

Principles  of  Construction. — The  masonry  dam  depends  for  its 
stability  upon  the  weight  of  its  component  particles,  and  also  upon 
the  cohesive  strength  between  these  particles.  It  may  be  regarded 
as  a  monolith  of  series  of  monoliths,  each  of  sufficient  weight  to  pre- 
vent its  overturning  due  to  the  pressure  of  the  water  and  also  having 
sufficient  cohesive  strength  between  the  parts  to  prevent  sliding  and 
to  a  certain  extent  permit  it  to  act  as  a  beam  or  arch. 

Comparing  the  masonry  dam  to  earth-  and  rock-fill  dams,  these 
may  be  arranged  in  a  series  according  to  the  relative  size  and  cohesive 
force  between  the  particles.  At  one  extreme  is  the  earth  dam  in 
which  each  grain  of  earth  or  sand,  or  pebble  of  gravel,  is  infinitely 
small  compared  to  the  total  mass  of  the  structure.  These  particles 
are  loosely  held  together  and  if  exposed  may  be  blown  away  by  the 
wind  or  washed  away  by  rain  or  running  water.  The  force  of  cohe- 
sion, if  regarded  at  all,  is  insignificant. 

Next  in  such  a  series  is  the  rock-fill  dam,  in  which  the  pieces  of 
which  it  is  composed  as  compared  to  those  of  the  earth  dam  are 
relatively  large,  many  of  them  being  of  sufficient  size  to  be  com- 
pared in  a  finite  sense  to  the  whole  volume  of  the  dam  and  so  heavy 
that  they  cannot  be  blown  by  the  winds  or  washed  away  by  running 
water.  With  the  masonry  dam  a  further  and  last  step  in  the  series 
has  been  taken  in  that  the  component  pieces  are  cemented  together 
to  form  a  single  large  mass,  or  at  least  to  make  a  few  blocks  forming 
an  appreciable  portion  of  the  whole  and  each  as  a  unit  capable  of 
withstanding  the  force  of  the  water  against  it. 

In  the  masonry  dam  there  is  a  factor  of  strength  due  to  the  condition 
that  a  section  of  the  dam  is  not  dependent  wholly  for  its  stability  upon 
the  weight  of  the  component  parts  considered  as  loose  particles.  Any 
vertical  section  standing  along  will  resist  a  force  tending  to  slide  it 
and  also  to  a  certain  extent  an  overturning  force  by  the  cohesion  of 
its  parts  the  section  being  considered  to  act  as  a  monolith  having 
resistance  to  crushing  and  shear.  Taking  a  horizontal  section  of  the 
masonry  dam  its  strength  is  increased  by  each  portion  acting  upon 

232 


MASONRY  DAMS  233 

those  adjacent  to  it  which  causes  it  to  behave  as  an  arch,  if  the 
structure  is  curved,  or  to  a  certain  extent  as  a  beam  or  cantalever  if 
the  structure  is  straight. 

In  designing  a  masonry  structure,  consideration  is  given  therefore 
not  only  to  the  weight  of  the  material  to  be  used,  but  to  the  form  of 
its  arrangement  and  especially  to  the  binding  together  of  the  parts 
to  resist  the  pressure  brought  against  the  whole  mass  and  which  tends 
to  overturn  or  lift  it. 

Kinds  of  Masonry  Dams. — Under  this  designation  of  masonry 
are  included  all  structures  which  are  built  of  large  or  small  blocks 
or  pieces,  laid  in  some  form  of  mortar  or  cement  to  cause  the  separate 
pieces  to  adhere.  There  are  thus  included  not  only  the  dams 
erected  of  carefully  quarried  and  dressed  stone  with  close-fitting 
joints  but  also  those  built  of  rough  fragments  not  dressed  to  specified 
dimensions  but  which  are  carefully  placed  in  mortar  or  cement 
in  such  way  as  to  form  tight  joints,  the  irregular  intervals  between 
the  large  blocks  being  partly  filled  by  smaller  stones  bedded  in  the 
mortar.  The  large  blocks  may  weigh  many  tons  or  the  material 
may  have  been  crushed  to  small  sizes,  in  which  case,  there  results 
a  dam  composed  of  concrete.  The  essential  factor  is  that  the  com- 
ponent masses,  whether  large  or  small,  shall  be  carefully  bedded 
and  surrounded  or  incorporated  in  mortar  or  cement,  so  as  to  form 
a  single  mass. 

An  apparent  exception  may  be  noted  where  the  masonry  dam  is 
built  with  expansion  joints  or  planes  of  weakness  dividing  the 
structure  into  large  sections,  each  of  which  is  interlocked  with  its 
neighbor  but  is  of  such  size  or  shape,  as  to  be  able  to  stand  alone — 
acting  as  a  separate  pier  or  beam. 

The  typical  masonry  dam  is  one  composed  of  carefully  selected 
rock,  quarry  dressed,  and  with  outer  covering  or  skin  on  the  upper 
and  lower  face,  made  of  selected  stones  cut  to  dimensions  such  as 
to  form  ashlar  masonry.  These  stones  or  especially  those  on  the 
upper  face  resisting  the  water  pressure  are  laid  with  extreme  care, 
so  that  there  will  be  as  little  leakage  as  possible  between  the  joints. 
The  interior  of  the  section  of  the  dam  is  usually  composed  of  as 
large  stones  as  can  be  handled,  laid  carefully  to  avoid  horizontal 
joints,  and  having  each  stone  well  bedded  against  its  neighbor, 
care  being  taken  to  keep  the  top  or  working  surface  as  rough  as 
possible  in  order  that  the  tendency  of  slipping  of  parts  of  the  struc- 
ture along  any  plane  may  be  avoided. 

Rubble  Concrete. — The  masonry  built  of  irregular  masses  of 


234      PRINCIPLES  OF  IRRIGATION  ENGINEERING 

rock  such  as  are  obtained  from  the  quarry,  fitted  into  place  without 
any  considerable  dressing  excepting  to  remove  loose  fragments 
is  included  under  the  terms  " rubble."  For  the  construction  of 
large  dams  rubble  carefully  laid  in  mortar  is  not  only  more  econom- 
ical but  is  preferable  to  the  ordinary  dressed  stone,  because  of  the 
fact  that  the  joints  between  the  rocks  are  irregular.  If  these  joints 
are  carefully  filled  with  mortar  or  cement  the  resulting  structure 
may  be  more  nearly  impervious  to  water.  The  dressing  of  the 
stones  from  the  quarry  and  attempting  to  bring  them  to  flat  sur- 
faces not  only  introduces  large  expense  but  unless  the  work  is  very 
carefully  done,  there  is  no  resulting  gain,  so  far  as  forming  an  impervi- 
ous joint.  The  smooth  surface  introduces  more  or  less  of  a  plane  of 
weakness  as  compared  with  the  rough  surface  where  one  stone 
projects  up  into  the  space  between  others. 

A  typical  rubble  masonry  dam  is  one  in  which  the  largest  possible 
stone  and  rock  are  used,  these  being  put  in  place  by  derrick  or  over- 
head cableways.  The  size  of  these  may  range  from  a  ton  up  to 
10  tons,  or  even  15  tons,  dependent  upon  the  strength  of  the  machin- 
ery. Each  large  stone  is  carefully  inspected  to  see  that  it  is  sound 
and  that  all  of  the  loose  fragments  have  been  removed.  It  is  then 
thoroughly  washed,  before  being  swung  into  place.  A  bed  of  soft 
mortar  has  previously  been  prepared  and  the  large  stone  is  placed 
carefully  in  it,  being  lifted,  if  necessary,  once  or  twice  to  see  that 
the  stone  bears  firmly  on  all  parts  of  the  mortar  bed.  Spalls  are 
then  rammed  in,  around  or  partly  under  the  rock,  where  possible 
and  another  bed  is  prepared  alongside  for  a  similar  large  rock, 
these  not  being  allowed  to  touch,  but  a  space  of  two  inches  or  more 
is  allowed  between  each  projecting  point.  The  result  is  what  in 
nature  would  be  called  a  coarse  breccia,  in  which  the  individual 
fragments  weigh  tons,  or  what  is  sometimes  called  a  "pudding 
stone"  in  which  the  "plums"  are  large  irregular  fragments.  For 
the  sake  of  appearances,  such  rubble  structures  are  usually  faced 
with  selected  rock,  or  the  projecting  inequalities  broken  off,  to 
bring  the  structure  within  neat  lines,  but  even  without  such  finish 
the  resulting  work  has  a  massive  roughness  consistent  with  its 
general  character. 

The  proportion  of  large  rock  in  Cyclopean  rubble  is  determined 
largely  by  the  question  of  expense.  If  the  large  pieces  each 
several  tons  in  weight  exceed  about  12  per  cent,  of  the  volume 
of  the  dam,  the  cost  tends  to  increase,  as  it  has  been  found  that  the 
time  required  to  make  the  joints  is  excessive  and  the  apparent 


PLATE  XV 


FIG.  A. — Earth  and  rockfill  dam  under  construction,  with  low  concrete  core 
wall,  gravel  and  earth  is  being  dumped  on  upper  side  with  loose  rock  below, 
Minidoka,  Idaho. 


FIG.  B. — Concrete  structure  for  regulating  floods.     East  Park  dam,  Orland 

Project,  Cal. 

(Facing  Page  234) 


PLATE  XV 


FIG.  C. — Rubble  masonry  dam;  lower  portion  of  Roosevelt  Dam,  Ariz.     (See 
finished  dam,  Plate  XI,  Fig.  D.) 


FIG.  D. — Foundations  for  Lahontan  Dam,  Nev.;  showing  concrete  conduit,  con- 
veying water  through  lower  part  of  dam,  with  conveying  plant  in  background. 


MASONRY  DAMS 


235 


gain  in  using  the  large  rock  is  counterbalanced  by  the  loss  of  time 
in  bedding  them. 

If  distinctly  stratified  rock  is  used  in  the  dam,  especially  any 
pieces  having  a  shaley  structure,  care  should  be  taken  not  to  bed 
these  horizontally,  but  to  place  the  rock  in  the  dam  in  a  vertical 
or  inclined  position  so  as  to  reduce  the  tendency  to  shear  along 
the  horizontal  planes. 

Foundations. — On  account  of  the  great  weight  of  a  masonry 
dam,  the  foundations  must  consist  of  solid  rock.  There  may  be 
exceptions  where  the  masonry  is  of  relatively  small  height  and  has 
great  breadth  of  base  or  bearing  surface,  in  which  case  it  may  be 
founded  upon  impervious  clays  or  even  on  sand  held  in  place  by 
sheet  piling  or  even  by  round  wooden  or  masonry  piles. 

In  preparing  the  foundation,  they  must  necessarily  be  laid  bare, 
the  water  being  excluded  by  a  cofferdam,  or  other  means  and  all  of 
the  looser  and  weaker  portions  of  the  rock  removed.  In  case  there 
are  open  cracks  or  seams  it  may  be  necessary  to  excavate  pockets  or 
shafts  to  a  depth  or  extent  such 
as  to  clean  out  all  of  the  poorer 
materials,  filling  in  the  cavities 
thus  made  with  carefully  placed 
concrete  or  masonry.  The  rock 
in  place  after  being  stripped  in  this 
way  is  left  as  rough  as  possible  in 
order  to  make  a  good  joint  and  is 
carefully  washed  to  remove  all  of 
the  smaller  particles  and  enable 
the  mortar  to  effect  a  complete 
bond. 

Section. — The  cross-section  of 
a  modern  masonry  dam  has  devel- 
oped into  a  somewhat  conven- 
tional    form     following     certain  FIG.  47. — Typical  section  of  masonry 
general    assumptions.     On    the  dam,  Boise  Project,  Idaho, 

upper  or  water  side  the  dam  is  nearly  vertical,  having  in  some  in- 
stances a  light  batter  or  forward  projection  of  about  i  ft.  horizontal 
to  20  vertical.  On  the  down-stream  side,  the  slope  is  about  i  ft. 
horizontal  to  from  1.5  to  2  ft.  vertical.  It  is  generally  a  straight 
line,  or  may  be  gently  curved,  the  batter  or  slope  being  increased 
downward  from  about  the  middle  height  of  the  dam  as  shown  in 
Fig.  47- 


236      PRINCIPLES  OF  IRRIGATION  ENGINEERING 


This  form  of  section  has  been  developed  from  theoretical  considera- 
tions, verified  by  practical  results.  There  are  two  principal  forces  to 
be  considered :  first,  the  downward  pressure,  or  weight  due  to  gravity 
of  each  portion  of  the  dam  acting  upon  the  foundation  or  upon  each 
horizontal  layer  or  section  of  the  dam;  and  second,  the  horizontal 
pressure  or  force  of  the  water  tending  to  push  the  dam  down-stream  or 
overturn  it.  There  are  other  forces,  such  as  "  uplift "  and  ice  thrust, 
of  less  immediate  importance,  but  which  are  to  be  considered. 

To  compute  the  resultant  of  the  two  main  forces,  the  dam  is  con- 
sidered as  consisting  of  an  indefinite  number  of  portions  formed  by 
taking  successively  lower  and  lower  sections  from  the  top  down  to  the 
foundation.  Beginning,  for  example,  with  the  first  10  ft.  of  the  top 


Fig.  48. — Location  of  dam  and  construction  camp,  Boise  Project,  Idaho. 

section,  the  center  of  gravity  of  the  assumed  section,  in  this  case 
usually  a  rectangle,  is  taken  and  the  downward  force  acting  through 
this  center  of  gravity  is  computed.  The  horizontal  pressure  of  the 
water  in  the  reservoir  when  full  is  also  ascertained  and  shown  as  act- 
ing upon  a  point  in  the  cross-section  one-third  of  the  height  of  the 
water  above  the  assumed  base.  The  lines  of  force  cross  at  right 
angles.  When  graphically  shown  (Fig.  49)  with  length  proportional 
to  the  relative  amount  of  pressure  in  each  case  they  enable  the  con- 
struction of  a  simple  triangle  of  forces  which  gives  the  direction  and 
amount  of  resultant  pressure. 

This  line  of  resultant  force  should  evidently  fall  within  the  base 
of  the  portion  of  the  dam  under  consideration,  otherwise  the  struc- 


MASONRY  DAMS 


237 


ture  might  be  overturned.  In  the  earliest  dams  built  the  thickness 
was  as  a  rule  made  excessive  and  the  resultant  line  fell  far  within  the 
section  so  that  evidently  there  was  a  large  waste  of  material.  The 
question  as  to  where  the  resultant  line  should  fall  has  been  under 
discussion  among  the  engineers  for  many  years,  it  being  primarily  a 
question  of  the  factor  of  safety  to  be  used.  There  has  finally  been 
adopted  as  more  or  less  of  a  compromise  a  somewhat  arbitrary  rule 
to  the  effect  that  the  resulting  line  of  pressure  with  the  reservoir  full 
or  empty  should  fall  within  the  middle  third  of  the  base  of  each  por- 


RinrE«d    E1.100± 


FIG.  49.  —  Graphic  computation  of  stresses  in  masonry  dam. 


tion  of  the  dam.  The  accompanying  Fig.  49  gives  graphically  the 
analysis  of  pressures  of  the  East  Park  Dam  of  the  Orland  project, 
California,  in  which  it  is  assumed  that  the  weight  of  concrete  is  140 
Ib.  per  cubic  foot,  the  weight  of  the  water,  62.5  lb.,  the  weight  of  the 
sand  and  gravel  in  river  bed,  100  lb.  per  cubic  foot.  The  only 
stresses  computed  were  those  due  to  the  dam  acting  as  a  gravity 
section.  The  figures  given  at  the  bottom  of  each  portion  of  this  sec- 
tion are  the  minimum  and  maximum  vertical  unit  stresses  per  square 


238      PRINCIPLES  OF  IRRIGATION  ENGINEERING 

inch  for  the  reservoir  full  and  empty.  The  general  location  of  this 
dam  is  given  in  Plate  XV,  Fig.  B. 

In  addition  to  the  ordinary  static  pressure  of  the  water  in  the  full 
reservoir  there  should  also  be  considered  in  the  case  of  dams  in  north- 
ern climates  the  probability  of  an  increased  pressure  at  the  surface 
due  to  the  formation  of  ice  on  the  reservoir.  What  this  pressure  may 
be  has  not  been  determined.  In  many  cases  it  is  probable  that  it  is 
so  small  as  to  be  negligible.  Observations  on  some  of  the  large  struc- 
tures show  that  the  ice  against  the  dam  is  very  thin,  or  in  some  cases 
there  is  open  water  throughout  the  winter.  The  surrounding  land 
may  be  in  such  shape  that  the  ice  pressure  if  any  is  exerted  along  the 
shore  line  and  not  appreciably  against  the  dam. 

The  maximum  amount  of  ice  pressure  that  has  been  assumed  is 
upward  of  44,000  Ib.  per  linear  foot.  This  adds  notably  to  the 
required  thickness  of  the  dam,  and  it  has  been  questioned  as  to 
whether  it  is  necessary  or  wise  to  make  provision  for  such  large 
assumed  forces. 

Concrete. — The  difference  between  rubble  masonry  and  concrete 
is  one  of  size  of  individual  stones  rather  than  of  essential  difference 
in  kind.  Instead  of  attempting  to  use  the  largest  possible  stones  in 
the  structure,  the  pieces,  are  crushed  to  a  small  and  nearly  uniform 
size,  and  then  mixed  with  the  mortar  or  cement,  so  as  to  produce  a 
mass  which  can  be  readily  handled  by  shovels  or  small  tools  or  which 
can  be  conveyed  or  allowed  to  flow  into  place  through  suitable 
conduits. 

One  of  the  great  advantages  of  concrete  construction  is  that  of 
possible  speed,  the  rate  of  depositing  the  concrete  being  dependent 
upon  the  size  and  economical  arrangement  of  the  crushing,  conveying 
and  mixing  machinery  which  may  be  relatively  compact;  whereas, 
in  the  case  of  masonry,  including  cyclopean  concrete,  the  speed  of 
construction  is  often  greatly  reduced  by  congestion  of  the  work  and 
necessity  of  installing  bulky  machinery  in  a  relatively  small  space, 
one  operation  interfering  with  or  delaying  another.  With  modern 
methods  of  mixing  and  delivering  concrete  into  place  through  con- 
duits, it  is  practicable  to  keep  flowing  to  the  dam  a  nearly  con- 
tinuous stream  without  one  portion  of  the  work  interfering  with 
another. 

This  speed  of  construction  is  an  important  consideration  in  the 
building  of  dams  in  localities  where  work  must  be  expedited  between 
flood  seasons.  By  having  made  in  advance  suitable  arrangements 
of  the  material  and  machinery,  it  is  practicable  to  lay  a  large  amount 


MASONRY  DAMS  239 

of  concrete  in  a  constricted  space  far  more  rapidly  and  economically 
than  could  be  done  in  the  case  of  large  blocks  of  stone. 

Another  advantage  possessed  by  concrete  over  ordinary  masonry 
is  that  the  mass  can  be  made  practically  homogeneous  and  the 
stresses  or  strains  in  the  finished  structure  may  be  more  nearly  antici- 
pated and  provided  for  by  suitable  expansion  joints  or  other  devices. 

Upward  Pressure. — No  masonry  or  concrete  structure  is  abso- 
lutely impervious  and  it  is  necessary  to  assume  that  water  will 
find  its  way  to  a  small  extent  under  the  foundations  and  into  the 
interior  of  the  dam.  In  many  of  the  modern  structures  elaborate 
drains  are  provided  to  carry  out  to  the  lower  side  the  water  which 
may  thus  occur  as  minute  springs  or  points  of  moisture.  In  addition 
to  this  certain  allowances  should  be  made  in  computing  the  strength 
of  the  structure  to  provide  for  the  accumulated  lifting  or  over- 
turning forces  of  the  water  which  may  percolate  under  or  through 
the  mass  and  not  freely  escape  at  the  lower  side. 

The  amount  of  this  upward  pressure  is  dependent  upon  the  height 
of  water  against  the  dam.  It  is  assumed  to  be  maximum  at  the 
water  face  and  to  decrease  to  nothing  at  the  lower  side.  In  com- 
puting the  overturning  forces  acting  upon  the  dam  allowance  should 
be  made  for  the  existence  of  this  force  and  the  thickness  of  the  dam 
correspondingly  increased  unless  perfect  drainage  is  provided. 

Curved  Dams. — Each  section  of  the  masonry  dam  is  usually 
computed  as  above  noted  on  an  assumption  that  it  is  to  stand 
alone,  without  aid  from  adjacent  vertical  sections,  but  wherever 
the  side  walls  or  abutments  are  sufficiently  firm  and  are  not  too 
far  apart,  it  has  been  the  custom  to  design  the  whole  dam  on  a 
curved  plan,  so  that  it  will  act  as  a  horizontal  arch,  transferring 
the  horizontal  pressure  of  the  water  in  part  from  section  to  section 
and  to  the  rock  abutments. 

The  radius  of  curvature  of  this  arch  is  generally  from  400  to 
600  ft.  but  may  be  more  or  less  than  this,  in  accordance  with  the 
length  of  the  dam. 

Multiple  Arch  Dams. — In  the  types  of  dams  already  described 
the  force  of  the  water  is  resisted  by  a  solid  mass  of  practically 
uniform  section  throughout  the  length  of  the  dam.  In  this  way  a 
maximum  of  material  is  used  and  the  question  naturally  arises  as 
to  whether  certain  portions  of  the  section  of  the  dam  cannot  be 
made  thinner  or,  to  consider  it  in  another  way,  whether  the  retaining 
wall  or  curtain  cannot  be  held  in  place  by  piers  or  buttresses,  rather 
than  by  continuous  mass  of  rock  or  earth. 


240      PRINCIPLES  OF  IRRIGATION  ENGINEERING 

This  is  particularly  the  case  with  concrete  construction,  where 
it  is  readily  seen  that  the  concrete  dam  being  composed  of  more 
or  less  plastic  material  may  be  moulded  into  any  form  desired. 
The  impervious  blanket  or  curtain  may  be  given  a  thickness  only 
sufficient  to  prevent  percolation  and  can  be  held  in  place  by  but- 
tresses or  struts  designed  of  ample  shape  and  form  to  hold  this 
curtain  against  the  pressure  of  the  water.  In  other  words,  we  may 
design  a  structure  upon  thoroughly  scientific  lines  and  without 
the  unnecessary  waste  of  material  which  is  found  in  the  usual  solid 
dam. 

These  multiple  arch  or  composite  dams  are  especially  suitable 
for  conditions  where  economy  of  material  is  a  prime  requisite  or 
where  the  foundations  are  of  a  somewhat  doubtful  character.  The 
saving  of  the  material  is  to  a  large  extent  offset  by  the  difficulties 
of  construction  and  in  many  cases  it  has  been  found  more  satis- 
factory to  build  the  more  simple,  solid  structure.  There  are, 
however,  a  number  of  types  of  composite  dams  which  are  coming 
into  favor,  in  which  the  back  or  water-tight  face  of  concrete,  usually 
reinforced,  is  supported  by  suitable  concrete  arches  or  pillars  upon 
a  foundation  or  base  adapted  to  the  character  of  the  underlying  rock. 

Internal  Stresses. — In  any  structure  where  the  masonry  is  laid 
under  varying  conditions  of  temperature  and  humidity,  there  must 
necessarily  develop  certain  inequalities  in  loading.  There  is  thus 
developed  strains  due  to  these  inequalities,  for  example,  the  masonry 
laid  during  the  extreme  heat  of  summer  when  everything  is  expanded 
must  necessarily  shrink  during  the  extreme  cold  of  winter..  For  this 
reason,  it  is  frequently  specified  that  masonry  structures  in  hot 
countries,  especially  those  portions  where  the  section  is  relatively 
thin,  shall  not  be  built  during  the  time  of  greatest  heat. 

The  largest  stresses  upon  the  masonry  dam,  especially  on  the  thin- 
ner portion  near  the,  top,  are  those  due  to  daily  change  of  tempera- 
ture. During  the  clear  nights  when  the  radiation  is  greatest,  the 
structure  cools  down  and  contracts.  The  morning  sun  may  strike 
upon  one  side  of  the  dam,  heating  it  rapidly,  while  the  other  side  is 
still  cold,  and  by  afternoon  the  conditions  may  be  reversed,  in  that 
the  opposite  side  is  exposed  to  the  hot  sunlight.  Thus  there  is  a  more 
or  less  continuous  though  minute  movement  of  the  structure  and 
tendency  to  form  temperature  cracks,  due  to  alternate  lengthening 
and  shortening  of  the  structure.  These  intensify  the  action  of 
the  waters  percolating  through  the  mass  from  the  upper  side,  and 
must  be  guarded  against  by  increased  thickness  above  what  would 


MASONRY  DAMS  241 

theoretically  be  sufficient.  The  drying  out  of  the  mass  of  concrete 
is  also  a  very  important  factor  in  developing  shrinkage  cracks. 

Safe  Limits  for  Foundations. — The  amount  of  load  which  a  founda- 
tion will  sustain  is  dependent  upon  the  texture  and  bedding  of  the 
rock.  A  fine-grained  granite,  for  example,  with  few  if  any  visible 
bedding  planes  and  held  in  place  by  the  weight  of  the  adjacent  strata 
is  practically  incompressible  and  will  stand  almost  any  weight  which 
can  be  put  upon  it.  On  the  other  hand,  porous  volcanic  rock  or 
strata  with  open  seams  may  be  readily  compressed  under  the  weight 
of  a  mass  of  masonry. 

It  is  customary  to  take  samples  of  the  material  under  considera- 
tion for  foundation  as  well  as  those  of  the  rock  to  be  used  for  the 
structure  and  to  apply  crushing  tests  to  determine  the  number  of 
pounds  or  tons  per  square  inch  required  to  fracture  the  stone.  This, 
of  course,  gives  certain  relative  values  for  small  samples  of  uniform 
size  and  texture  but  does  not  demonstrate  how  the  rock  will  behave 
in  large  masses  or  when  prevented  from  moving  or  expanding  later- 
ally, as  for  example  when  in  place  and  held  by  adjoining  rock. 

Based  on  the  above  assumptions  the  safe  limits  for  foundations  and 
for  material  for  masonry  dam  have  been  taken  as  from  25  to  30  tons 
per  square  foot  or  400  Ib.  per  square  inch  that  is  to  say,  in  computing 
the  weight  upon  the  foundations  and  in  designing  the  thickness  of 
section  of  the  dam,  this  has  been  increased  until  the  pressure  per 
square  foot  of  the  superimposed  mass  will  not  exceed  the  figures 
given.  In  this  case,  it  is  assumed  that  upon  each  square  foot  of 
bearing  surface  there  will  be  imposed  the  weight  of  a  shaft  i  ft. 
square  and  extending  to  a  depth  of  the  dam,  plus  the  added  pressure 
due  to  the  component  forces  which  may  tend  to  overturn  the  dam 
and  thus  increase  the  pressure  upon  this  point. 

As  a  matter  of  fact,  owing  to  the  slight  inequalities  in  bearing  a 
somewhat  greater  pressure  may  be  imposed  upon  one  square  foot  or 
small  area  and  correspondingly  removed  from  another,  so  that 
compression  or  crushing  to  a  small  extent  must  take  place  before 
every  square  foot  of  the  surface  is  brought  into  absolutely  equal 
bearing. 

The  data  upon  the  strength  of  various  rocks  have  been  obtained 
largely  from  tests  made  upon  cubes  of  i  in.  or  2  in.  on  edge.  These 
show  that  under  compression  these  cubes  will  withstand  a  weight 
of  from  20,000  to  40,000  Ib.  or  even  more  per  square  inch,  or  from  10 
to  20  tons.  It  is  probable  that  in  larger  masses  of  indefinite  extent 
the  ability  to  resist  crushing  would  be  still  greater.  With  limestone 

16 


242      PRINCIPLES  OF  IRRIGATION  ENGINEERING 

likewise,  the  crushing  strength  for  small  cubes  has  been  ascertained 
to  be  from  14,000  to  20,000  Ib.  per  square  inch  or  from  7  to  10  tons. 

Where  the  material  underlying  the  foundation  is  relatively  soft  or 
porous,  the  foundations  must  be  spread  correspondingly  to  distribute 
the  load,  so  that  there  can  be  no  notable  settlement  after  the  struc- 
ture is  finished.  Such  settlements  may  result  from  either  one  of  two 
principal  causes;  first,  the  actual  compression  vertically  of  the  rock 
by  which  minute  openings  or  joints  are  closed,  or  softer  particles 
decreased  in  bulk  or,  second,  by  the  gradual  flow  of  some  of  the 
lower  layers.  It  is  well  known  that  even  apparently  solid  rocks 
under  great  stress  are  slightly  plastic  and  if  around  the  sides  of  the 
foundations  the  rocks  are  not  confined  and  held  in  place  by  adjacent 
rocks  of  equal  hardness,  there  will  be  a  tendency  to  flow.  If  properly 
held,  however,  even  the  softest  rocks  will  sustain  heavy  weights  as 
shown,  for  example,  by  the  action  of  partly  consolidated  sandstone, 
or  even  of  sand,  which  if  held  from  lateral  movement  will  sustain  a 
large  load. 

Overflow  Dams. — Where  the  masonry  is  designed  to  be  over- 
topped by  water,  provision  must  be  made  not  only  for  the  increase 
in  water  pressure  against  the  dam  but  also  for  the  increased  weight 
upon  the  structure  due  to  carrying  the  water  and  also  to  the  change 
of  distribution  of  load.  The  most  important  consideration,  however, 
is  that  of  absorbing  the  energy  of  the  falling  water  in  such  way  that 
it  will  not  injure  the  dam  either  by  direct  erosion  or  by  undercutting 
of  the  toe  or  by  impact  or  shock. 

The  conventional  type  of  overflow  dam  is  that  with  gently  curving 
lower  side  on  which  the  water  overflowing  the  crest  glides  downward 
over  the  smooth  surface  and  is  gently  deflected  from  a  nearly 
vertical  drop  to  a  horizontal  direction.  The  accompanying  Fig. 
50.  gives  the  general  outline  of  such  a  dam,  together  with  the 
graphic  analysis  of  the  stresses.  In  estimating  the  forces  acting 
upon  the  dam  the  assumption  is  made  that  the  concrete  weighs 
147  Ib.  per  cubic  foot,  that  it  contains  20  per  cent,  of  rock  and  that 
the  weight  of  the  rock  is  156  Ib.  per  cubic  foot,  the  average  weight 
of  the  mixture  in  the  dam  being  149  Ib.  per  cubic  foot.  The  water 
is  assumed  to  weigh  62.5  Ib.  per  cubic  foot  and  the  flowing  mud 
57  1/2  Ib.  per  cubic  foot  additional. 

The  figure  under  discussion  is  a  section  of  the  Granite  Reef  Dam 
on  Salt  River  project,  Arizona.  It  is  provided  with  a  tight  concrete 
curtain  wall  6  ft.  wide  under  the  upper  face  of  the  dam,  and  another 
curtain  wall  with  wide  holes  to  permit  water  to  escape  which  may 


MASONRY  DAMS 


243 


have  penetrated  beneath  the  dam.  On  the  upper  section  the  area 
is  estimated  at  184  sq.  ft.  and  the  weight  of  a  section  i  ft.  thick  is 
given  as  27,416  Ib.  On  this  the  horizontal  liquid  pressure  is  esti- 
mated at  24,750  Ib.,  and  vertical  liquid  pressure  at  5,040  Ib. 

The  curved  section  is  designed  on  the  theory  that  the  water 
should  be  forced  to  move  in  parallel  lines  down  along  the  dam  and 


Assumed  High  Water  Elev.1322 


r 


W.S.  Probable 
Backwater 


k 


below  Apron 


For  fallinglbodj 
with  initial  HorU.relocitj 
12>^fl.p.ri«j.;dfc=22.'j 


V=  40.  ft-p«  Mo.(»bt.) 
O  =  abt.l5u  ca.a.per  sac 
I5Ui«2.5  l4a  =  11818 

__?__4-_-- 


'^H6-J 
Elev.1290  i 


j    Curtain  Wall      | 

[UM  WMP  holw  in  Jti-^ •' 


FIG.  50.  —  Cross-section   of   overflow   dam   with   graphic  analysis  of  stresses, 
Granite  Reef  Dam,  Salt  River  Project,  Arizona. 


then  be  deflected  to  flow  directly  away  from  it.  This  theory  is 
followed  out  very  well  so  far  as  the  behavior  of  the  water  on  the 
face  of  the  dam  itself  is  concerned,  but  after  the  direction  is  changed 
to  a  point  where  it  should  leave  the  dam,  there  is  usually  a  retarda- 
tion resulting  in  a  standing  wave  which  offers  a  number  of  curious 
phenomena.  The  water,  instead  of  continuing  with  gradually 
reduced  velocity  down-stream,  gathers  in  a  mass  on  the  apron  of 


244      PRINCIPLES  OF  IRRIGATION  ENGINEERING 

the  dam  and  sets  up  a  churning  or  rotary  motion  which  threatens 
to  undercut  the  apron  if  near  the  lower  edge. 

Because  of  the  difficulties  involved  by  the  standing  wave  or 
whirlpool  at  the  lower  toe  of  the  overflow  masonry  dams,  this 
type  of  dam  has  been  made  in  many  cases  to  depart  from  the  con- 
ventional curve  and  to  drop  the  water  more  nearly  vertically 
rather  than  attempt  to  shoot  it  away  from  the  dam  in  the  horizontal 
lines.  In  this  case,  it  is  necessary  to  make  the  cross-section  of 
the  dam  such  that  water  flowing  over  the  crest  drops  into  a  deep 
pool  or  water  cushion.  In  descending  vertically  it  strikes  the 
return  currents  thus  breaking  up  the  force  of  water  by  work  per- 
formed upon  itself. 

Protection  of  Lower  Toe  from  Erosion. — The  vulnerable  point 
of  most  overflow  dams  is  at  the  lower  or  down-stream  toe.  The 
character  of  the  protection  of  this  determines  largely  the  profile 
of  the  lower  side  of  the  dam.  If  it  is  determined  to  deliver  the  water 
into  the  stream  in  a  horizontal  direction  it  is  necessary  to  provide 
an  apron  extending  down-stream  for  a  considerable  distance  below 
the  dam.  The  length  of  apron  required  is  of  course  dependent 
upon  the  height  of  overflow  and  the  volume  of  water  passing  over 
the  dam.  The  lower  end  of  this  apron  in  turn  is  usually  protected 
by  heavy  rock  pavement,  but  even  with  the  most  elaborate  device 
there  is  liable  to  occur  erosion  of  the  bottom  and  sides  wherever 
there  is  a  point  of  weakness.  This  is  due  to  the  whirling  or  gyratory 
movement  of  the  water  set  up  in  changing  its  velocity  and  cross- 
section  from  that  acquired  by  the  fall  over  the  dam  to  the  relatively 
slower  movement  in  the  horizontal  channel. 

Various  arbitrary  rules  have  been  given  for  the  length  of  the  apron, 
such,  for  example,  that  this  should  be  five  or  ten  times  the  height  of 
the  overfall,  but  in  most  cases  the  apron  has  been  built  of  what  is 
considered  reasonably  safe  length,  and  then  as  experience  is  had, 
it  has  been  lengthened  by  protecting  the  lower  end. 

In  the  case  of  structures  which  are  designed  on  the  opposite 
principle,  namely,  that  of  receiving  into  the  stream  channel  the 
water  falling  directly  over  the  dam,  an  entirely  different  arrangement 
is  necessary.  Instead  of  a  smooth  sloping  apron  a  deep  pool  or 
water  cushion  is  provided  with  walls  of  sufficient  strength  to  resist 
the  shock  of  the  falling  water.  The  theory  of  this  form  of  construc- 
tion is  that  the  water  should  be  forced  to  impinge  upon  itself  and  not 
upon  any  hard  substance.  The  container  therefore  must  be  of 
sufficient  size  and  strength  so  that  the  rotating  or  gyrating  water 


MASONRY  DAMS  245 

in  the  pool  will  have  sufficient  volume  to  cushion  the  effect  of  the 
fall  without  expending  energy  immediately  on  the  walls. 

Safe  Heights. — The  heights  of  masonry  dams  have  been  steadily 
increased  and  larger  structures  each  year  are  being  designed  on 
the  basis  of  experience  attained  in  building  and  operating  the 
previously  finished  works.  As  in  the  case  of  ships  or  other  structures 
each  decade  appears  to  see  the  limit  of  size,  but  this  is  quickly 
surpassed  by  the  next  design.  Theoretically,  there  is  no  limit 
to  size,  as  a  masonry  dam  is  an  artificial  reproduction  of  a  hill  or 
dike,  such  as  those  built  by  nature  to  heights  of  thousands  of  feet. 
It  is  merely  a  question  of  using  enough  material  properly  put  to- 
gether, the  size  being  governed  by  the  relation  between  the  cost 
and  the  value  of  the  result. 

With  increase  of  depth  and  consequent  hydraulic  pressure  upon  the 
natural  cracks  or  pores  in  the  foundations,  and  upon  the  joints  in 
the  masonry,  it  is  necessary  to  observe  greater  precautions  both  in 
closing  these  cracks  and  in  providing  adequate  weight  and  breadth 
of  foundation  to  afford  an  ample  factor  of  safety.  In  building  a  very 
high  dam  all  of  these  matters  are  necessarily  given  greater  study 
and  consideration  than  in  the  case  of  the  smaller  works.  The 
failures  which  have  taken  place  have  been  of  relatively  low  structures 
in  which  the  problems  seemed  so  simple  that  they  have  been  neglected 
and  the  proper  precautions  have  not  been  taken  or  the  fundamentals 
carefully  worked  out  on  a  theoretical  and  practical  basis  as  on  the 
higher  structures. 

Typical  Masonry  Dams. — The  best-known  masonry  dams  are 
those  which  have  been  built  in  connection  with  the  water  supply  of 
large  cities  notably  the  dams  on  the  Croton  watershed  for  the  city  of 
New  York,  those  of  the  Sudbury  River  for  Boston,  and  those  in  the 
vicinity  of  San  Francisco.  More  recently  several  notable  structures 
have  been  designed  and  built  by  the  Reclamation  Service,  particu- 
larly the  Roosevelt  Dam  in  Arizona  and  the  Shoshone  and  Path- 
finder in  Wyoming. 

The  following  list  gives  the  location,  name  and  type  of  the  principal 
storage  and  diversion  dams,  whether  of  masonry  or  earth,  constructed 
by  the  Reclamation  Service,  together  with  the  maximum  height,  the 
length  and  the  volume  of  the  dam  in  cubic  yards.  The  largest 
structure  as  far  as  cubical  contents  is  the  earth  dam  across  Owl 
Creek  on  the  Belle  Fourche  project  in  South  Dakota,  containing 
1,600,000  cu.  yd.  of  earth.  Next  in  order  to  this  are  the  Lower  and 
Upper  Deerflat  Embankments,  Idaho,  also  earth  dams,  and  then  the 


246      PRINCIPLES  OF  IRRIGATION  ENGINEERING 

Cold    Springs    Dam,   also  of  earth,   on  the   Umatilla  project  in 
Oregon. 

The  largest  of  the  masonry  dams  is  that  on  the  Salt  River  project 
in  Arizona,  the  Roosevelt,  containing  342,000  cu.yd.  of  masonry  with 
a  height  of  280  ft.  In  comparison  with  this  the  Shoshone  Dam  in 
Wyoming,  with  a  height  of  328  ft.,  contains  only  75,000  yd.  of  con- 
crete, and  the  Pathfinder,  218  ft.  high,  on  the  North  Platte  River, 
in  Wyoming,  contains  a  little  over  60,000  cu.  yd. 


MASONRY  DAMS 


247 


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CHAPTER  XVII 
OUTLET  WORKS 

Capacity. — The  capacity  of  the  outlet  of  a  reservoir  or  the  means 
of  drawing  down  the  stored  supply,  must  be  ample  to  provide  for 
the  largest  probable  demand  which  will  be  made  for  water  for  irri- 
gation and  power  purposes.  In  considering  the  size  of  outlet,  ac- 
count must  be  taken  of  the  fact  that  it  may  be  necessary  to  draw  a 
full  supply  when  the  water  in  the  reservoir  is  low  and  the  head  on 
the  outlet  comparatively  small.  For  this  reason  computations  for 
capacity  of  outlet  should  be  based  upon  a  minimum  head  in  the 
reservoir.  It  is  assumed  that  ample  provision  is  made  for  a  spill- 
way capacity  for  floods  but  it  may  be  desirable  or  even  necessary 
to  supplement  this  spillway  by  large  capacity  of  outlets  because  of 
the  fact  that  these  draw  water  from  the  lower  part  of  the  reservoir 
if  not  too  deep,  and  thus  aid  to  a  certain  extent  in  keeping  it  clean 
by  permitting  the  heavier  muddy  waters  to  escape.  The  spillways 
skim  off  the  surface  of  the  less  muddy  water;  if  the  flood  discharged 
is  wholly  over  them,  there  is  a  tendency  for  the  mud  and  silt  carried 
down  by  the  floods  to  be  deposited  in  the  deeper  part  of  the  reser- 
voir near  the  dam.  Where  practicable  as  much  of  this  deposit  as 
possible  should  be  drawn  off  through  the  lower  outlets. 

Location. — Experience  has  shown  that  outlet  works  for  a  deep 
reservoir  should  be  located  at  various  heights.  Where,  for  example, 
the  depth  of  water  is  considerably  over  100  ft.  dependence  should 
not  be  placed  wholly  upon  the  sluices  or  gates  placed  near  the 
bottom  of  the  reservoirs,  as  these  are  apt  to  be  partly  buried  in  mud 
or  silt.  The  erosive  effects  of  the  muddy  waters  under  this  head  is 
also  so  great  that  few  materials  can  withstand  it.  In  planning  the 
outlet  works,  therefore,  arrangements  should  be  made  to  draw 
water  under  heads  of  not  to  greatly  exceed  60  to  70  ft.  and  to  use 
the  lower  sluices  only  when  the  reservoir  has  been  drawn  down  to  a 
considerable  degree,  or  when  it  may  be  necessary  to  flush  the  lower 
portion  of  the  reservoir  immediately  adjacent  to  the  dam. 

The  location  of  the  outlet  works  must  be  governed  largely  by 
consideration  of  the  safety  of  the  structure.  Wherever  practicable, 
they  should  be  built  in  tunnel  in  the  natural  rock  of  the  side  walls. 

248 


OUTLET  WORKS 


249 


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250      PRINCIPLES  OF  IRRIGATION  ENGINEERING 

Occasionally  conditions  are  such  that  it  is  necessary  to  put  the  out- 
let through  the  dam  or  on  the  foundations.  In  such  cases  extra- 
ordinary precautions  must  be  taken  to  prevent  water  following  along 
the  outlet  conduits  or  pipes,  and  to  guard  against  any  unequal 
settling  of  the  dam,  due  to  this  point  of  weakness. 

Location  of  Gates. — The  gates  which  control  the  outlet  of  a 
reservoir  should  be  so  located  that  when  closed  they  exclude  water 
from  entering  the  conduit  or  channel  through  which  water  is  to  be 
discharged.  This  is  usually  accomplished  by  locating  the  gates  at 
the  upper  end  as  shown  in  Fig.  51.  If  the  gates  are  placed  far  back 
in  the  body  of  the  dam,  the  water  standing  against  them  when 
closed  exerts  the  full  pressure  of  the  reservoir  head  on  the  walls 
of  the  conduit  and  may  find  entrance  into  the  dam  itself  by  per- 
colation through  these  walls.  For  dams  with  flat  up-stream  slopes 
the  placing  of  the  gates  at  the  upper  end  of  the  outlet  conduit 
renders  them  more  or  less  difficult  of  access. 

The  two  conditions  of  accessibility  and  safety  are  combined  with 
difficulty  and  it  is  sometimes  necessary  to  have  more  or  less  of  a 
compromise.  As  a  rule,  the  gates  are  protected  by  being  installed 
within  a  solid  masonry  chamber  as  near  as  possible  to  the  upper  face 
of  the  dam,  the  chamber  walls  being  projected  upward  into  a  tower 
within  which  the  necessary  mechanism  is  located.  The  usual 
practice  is  to  provide  the  upper  end  of  each  outlet  with  valves  or 
gates  in  duplicate,  so  that  if  one  set  fails  the  other  can  be  operated. 
There  is,  however,  opposition  to  this  course,  as  it  has  been  urged  that 
these  gates  may  be  multiplied  indefinitely  without  eliminating  all 
risk  of  failure.  In  the  recently  designed  Arrowrock  Dam  on  the 
Boise  River,  Idaho,  an  exceedingly  strong  gate  protected  by  a  grill- 
age is  to  be  placed  near  the  up-stream  face  to  be  used  as  a  bottom 
sluice  and  not  to  be  opened  under  a  head  of  over  60  ft.  There  are 
also  to  be  built  in  the  lower  portion  of  the  dam  several  gates  at  vari- 
ous elevations,  each  being  supplied  with  an  independent  conduit. 
Each  of  these  openings  can  be  closed  by  means  of  stop  planks  at 
low  stages  of  the  reservoir  and  repairs  made  to  the  gates.  By  this 
means  they  are  rendered  more  accessible  than  would  be  the  case 
if  placed  in  a  tunnel. 

Gate  Towers. — Access  to  the  gates  controlling  the  outlets  to  reser- 
voirs is  usually  provided  by  means  of  vertical  towers  or  shafts 
supported  on  top  of  the  gate  chambers  and  carried  up  above  the  high- 
water  level.  Where  the  upper  face  of  the  dam  is  vertical,  or  nearly 
so,  as  in  the  case  of  a  masonry  dam,  the  gate  tower  is  usually  built 


OUTLET  WORKS 


251 


G 

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IS 


252      PRINCIPLES  OF  IRRIGATION  ENGINEERING 

against  it.  In  some  instances  access  to  the  gates  is  provided  by 
means  of  a  shaft  built  in  the  body  of  the  dam.  This,  however,  may 
introduce  complications  both  of  reaching  and  operating  the  gate 
and  possible  unequal  settlement  of  the  structure. 

For  earth  or  rock-fill  dams  with  flat  upper  slopes,  the  gate  tower 
is  generally  carried  up  as  an  independent  structure,  access  to  it 
being  provided  by  means  of  a  bridge  either  from  the  shore  or  top 
of  the  dam.  In  some  cases  inclined  valves  have  been  tried,  such  that 
the  operating  mechanism  lies  along  the  sloping  upper  face  of  the  dam 
as  shown  in  Fig.  52.  A  disadvantage  of  these  is  the  difficulty  of 
operating  and  inspecting  in  this  inclined  position.  In  cold  climates 
some  difficulty  has  been  experienced,  due  to  the  pressure  of  ice 
against  gate  towers  constructed  independent  of  the  dam.  The 
strength  which  a  tower  must  have  to  resist  the  pressure  of  ice  under 
varying  conditions  is  difficult  to  determine  with  certainty. 

Openings  to  gate  towers  are  usually  provided  so  that  water  may  be 
drawn  from  various  elevations  in  the  reservoir.  Occasionally  the 
tower  is  divided  into  compartments  so  that  water  can  be  shut  off 
from  one  or  other  of  the  gates  and  drawn  out,  permitting  inspection 
and  repairs. 

Operation  of  Gates. — The  gates  or  valves  of  low  dams  are  operated 
usually  by  a  screw  lifting  device,  the  stem  of  the  screw  being  con- 
tinued upward  through  the  masonry  or  within  the  tower  to  a  point 
above  high- water  level  where  suitable  capstan  or  other  mechanism 
for  raising  and  lowering  the  gates  is  installed. 

Where  the  depth  of  the  reservoir  is  very  considerable,  or  over  say 
60  ft.,  vertical  hydraulic  devices  have  been  successfully  tried  for 
operating  the  gate,  these  being  driven  by  small  pump  or  motor.  The 
piston  in  this  case  is  located  as  nearly  as  possible  above  the  gates  to  be 
raised  and  the  piston  rod  operates  through  a  stuffing  box  leading  from 
the  top  of  the  gate  into  a  water-tight  chamber  immediately  over  the 
top  of  the  gates. 

Erosion  due  to  High  Velocities. — Large  gates  or  valves  under  high 
pressure  offer  a  number  of  problems  and  require  special  design. 
The  two  chief  points  of  difficulty  encountered  are,  first,  the 
erosion  due  to  water  issuing  through  the  gates  under  high  velocity, 
especially  when  carrying  mud  or  sand,  and  second,  the  vibration  or 
chattering  of  the  gates  due  to  the  current  of  the  water  passing  over 
the  sharp  edges,  or  around  angular  material. 

There  are  some  curious  phenomena  in  connection  with  erosion. 
On  the  one  hand  the  hardest  of  materials  may  be  rapidly  cut  by  the 


PLATE  XVI 


FIG.  A. — Gate  tower  and  bridge  from  earth  dam,  forming  Cold  Springs  Reser- 
voir.    Umatilla  Project,  Ore. 


FIG.  B. — Grillage  protecting  entrance  to  gates.     Pathfinder  Reservoir.     North 
Platte  Project,  Wyo. 

(Facing  Page  252) 


PLATE  XVI 


FIG.  C. — Spillway  with  effective  lengths  increased  by  curved  outlines.     Orland 

Project,  Colo. 


FIG.  D. — Spillway  for  earth  dam.     Belle  Fourche  Project,  So.  Dak. 


OUTLET  WORKS  253 

sand  blasts  and  the  best  concrete  carved  into  fantastic  forms;  on 
the  other  hand  moss  may  be  found  growing  on  the  edge  of  channels 
where  such  velocities  are  obtained.  The  problem  is  largely  that  of 
the  character  of  the  internal  motions  caused  by  the  form  of  the 
orifice.  This  is  illustrated  in  the  case  of  a  jet  or  nozzle  where  it  has 
been  shown  that,  for  example,  with  a  needle  nozzle  and  with  a  certain 
shape  of  bucket  of  water  wheel,  the  water  will  issue  in  straight  lines 
and  be  deflected  with  the  minimum  erosion;  whereas,  witji  a  slightly 
differing  form  of  outlet  internal  currents  are  set  up,  causing  a  large 
amount  of  wear. 

Experience  has  shown  that  the  conduit  leading  away  from  any 
large  gate  or  valve  operating  under  high  pressure  should  have  as 
direct  and  straight  an  opening  to  the  outer  air  as  possible  and  with  a 
slight  constriction  beyond  the  gates  so  that  the  maximum  pressure 
will  be  borne  by  the  outlet  conduit  and  not  by  the  gate  itself  when 
wide  open. 

Vibration  of  Gates. — All  forms  of  valves  in  which  a  portion  is  under 
tension  are  subject  to  serious  vibration.  For  this  reason  the  balanced 
or  needle  valves  with  all  the  material  in  compression  are  preferable 
wherever  they  can  be  used.  The  tendency  to  vibrate  is  reduced  and 
the  wave  movement  is  rendered  practically  negligible  in  well-designed 
valves  of  this  character.  The  cause  of  vibrations  may  be  attributed 
to  three  different  classes  of  forces  which  when  acting  alone  may  be 
negligible  but  when  acting  in  unison  produce  serious  results.  Each 
of  these  tends  to  cause  a  certain  amount  of  motion,  which  may  be 
neutralized  in  part  by  the  other  but  when  by  chance  the  time  inter- 
val happens  to  coincide  the  motion  is  amplified. 

The  forces  causing  vibration  may  be  divided  into  three  classes: 

(1)  Wave  action. 

(2)  Pendulum  action. 

(3)  Reed  action. 

(i)  The  wave  action  or  rather  the  interval  of  action  is  that  due  to 
the  length  of  wave  in  the  water.  It  is  assumed  that  the  velocity  of 
wave  motion  in  the  open  air  is  1,090  ft.  per  second.  In  the  more 
dense  medium  of  fresh  water,  the  velocity  of  the  pressure  wave  is 
generally  taken  at  about  4,500  ft.  per  second  in  an  open  body  of 
water  such  as  a  lake,  while  a  safe  average  in  concrete-lined  conduits 
may  be  taken  as  3 ,300  ft.  per  second.  This  pressure  wave  is  set  up  on 
the  occurrence  of  a  slight  disturbance  or  motion  of  the  gate  and 
continues  indefinitely. 


254      PRINCIPLES  OF  IRRIGATION  ENGINEERING 

(2)  Any  sliding  gate  hung  vertically  becomes  in  effect  a  pendulum 
having  a  very  slight  range  of  swing.     If  this  pendulum  length  happens 
to  coincide  in  some  simple  arithmetical  relation  with  the  length  of 
the  pressure  wave  and  thus  the  two  happen  to  act  in  unison,  the  in- 
tensity of  the  motion  is  increased. 

(3)  The  lower  edge  of  the  partly  opened  gate  being  supported  at 
each  side  acts  as  a  beam  and  the  edge  partakes  of  the  nature  of  a 
reed  such  as  that  of  an  organ  but  having  an  extremely  low  tone  or 
rate  of  vibration.     This  vibration  following  the  laws  of  harmonics 
may  be  synchronous  at  intervals  with  the  pressure  wave  and  pendu- 
lum motion  so  that  it  may  be  conceivable  that  these  three,  namely, 
the  pressure  wave,  the  pendulum  wave  and  the  reed  wave  may  at 
some  interval  occur  on  the  same  beat  and  their  amplitude  or  destruc- 
tive action  be  thus  greatly  increased. 

Observation  has  shown  that  on  structures  even  of  great  solidity  the 
opening  of  the  gates  to  a  certain  point  causes  vibrations  to  be  set  up 
and  transmitted  to  a  distance  such  as  to  be  terrifying  to  the  observer, 
destructive  to  lighter  machinery,  and  possible  to  the  structure  itself. 
When,  however,  the  gates  are  raised  or  lowered  out  of  this  particular 
position,  the  vibrations  are  reduced  and  continue  with  more  or  less 
magnitude,  according  to  the  dimensions  and  shape  of  the  outlet. 

This  vibration  or  chattering  of  large  gates  under  high  head  is 
comparable  in  part  to  the  action  of  the  steam  whistle,  in  which  a 
current  of  air  or  steam  striking  a  thin  plate  or  reed  causes  it  to  spring 
forward,  then  it  reacts  backward  through  a  minute  space,  these 
alterations  following  with  such  great  speed  as  to  set  up  waves  pro- 
ducing sound.  In  the  case  of  the  gate,  instead  of  the  vibrating  reed 
we  have  a  very  large  structure  set  in  relatively  slow  vibration  so  that 
each  individual  impact  is  noticeable. 

The  vibrations  are  dependent  upon  the  degree  to  which  the  gates 
are  opened.  As  the  gate  is  raised  from  its  seat  the  motion  begins 
slightly  and  usually  reaches  its  maximum  with  a  half-opened  or 
three-quarter  aperture,  ceasing  as  the  gate  is  pulled  back  into  its 
recess,  unless  the  lower  edge  is  fully  exposed  to  the  current  of  water. 

The  continuous  vibration  tends  to  loosen  every  joint  and  bolt, 
finding  every  point  of  weakness  so  that  in  some  cases  it  is  necessary 
to  open  the  gate  completely  or  open  and  close  it  at  short  intervals, 
in  order  to  save  the  structure.  The  vibration  when  the  gate  is  fully 
open  can  be  guarded  against  as  before  stated  by  having  a  constric- 
tion in  the  solid  conduit  beyond  the  gate. 

Character   of   Gates. — The   lowest   outlets   for   deep   reservoir, 


OUTLET  WORKS  255 

especially  where  liable  to  be  buried  in  sediment,  should  have  rectangu- 
lar slide  gates  without  roller  or  other  complicated  form  of  bearing. 
It  has  been  found  advisable  to  use  relatively  broad,  firm  bearing 
strips  of  composition  metal  somewhat  of  the  character  of  bronze, 
the  two  surfaces  being  made  of  slightly  different  composition  for 
the  reason  that  if  both  bearing  faces,  namely  that  on  the  frame 
and  that  on  the  valve,  are  identical  in  composition  there  is  a  tendency 
to  "freeze"  in  that  the  two  metal  surfaces  of  identical  character 
under  this  high  head  cohere  probably  through  molecular  action. 
If,  however,  there  is  a  slight  difference  in  composition  the  molecular 
structure  appears  to  have  sufficient  difference  to  prevent  this  so- 
called  freezing. 

These  gates  may  be  raised  vertically  by  stems  operated  by  oil- 
pressure  cylinders  protected  in  such  way  as  to  prevent  the  entrance 
of  grit.  The  square  form  of  gate  has  been  found  most  desirable 
as  against  the  round  seat,  as  this  affords  a  more  perfect  sliding 
surface  and  has  less  tendency  to  displacement  when  the  gate  is 
partly  open.  For  higher  valves  not  buried  in  sediment  various 
forms  of  needle  valves  are  preferable.  All  regulation  of  the  full 
reservoir  should  be  done  with  valves  of  this  character. 

The  lower  slide  valves  or  gates  of  the  reservoir  should  never 
be  used  for  regulation  but  if  necessary  to  open  them  they  should 
be  drawn  completely  back  into  their  sockets  and  not  allowed  to 
remain  in  a  partly  open  position  on  account  of  the  excessive  erosion 
and  vibration  which  is  set  up.  The  opening  as  before  stated  should 
be  into  as  nearly  a  straight  smooth  conduit  as  possible,  gradually 
changing  from  rectangular  form  at  the  gate  to  circular  form  and 
lined  both  above  and  below  the  valve  with  cast-iron  pipe  and  con- 
tinued by  concrete  slightly  diminishing  in  sectional  area  until  the 
conduit  is  at  least  25  per  cent,  smaller  than  the  opening  of  the  gate. 

Where  there  are  several  gates  each  should  open  into  a  separate 
conduit  and  these  conduits  should  not  unite  but  continue,  each 
independently  to  the  outer  air. 

One  of  the  important  details  of  closure  of  flat-slide  valves  or  gates 
of  this  kind  is  in  the  character  of  the  contact  of  the  lower  edge. 
As  this  approaches  the  seat  or  bottom  the  scouring  effect  under 
the  gate  is  greatly  increased  and  ordinary  metal  is  quickly  cut  out 
or  destroyed.  It  has  been  found  by  experience  that  a  relatively 
soft  seat  composed  of  a  bar  of  lead  or  even  of  timber  if  depressed 
slightly  below  the  floor  will  not  be  notably  eroded  and  permits 
the  seating  of  the  gate  and  complete  closure  even  under  high  heads 


256      PRINCIPLES  OF  IRRIGATION  ENGINEERING 

or  unfavorable  surroundings.  The  type  of  gate  seat  thus  found 
most  advantageous  is  one  where  a  groove  is  filled  with  a  lead  base, 
the  top  of  which  is  depressed  slightly  below  the  floor  line. 

In  order  to  overcome  the  difficulties  due  to  high  heads  a  type 
of  balanced  valve  has  been  successfully  used  on  several  of  the 
reservoirs  built  by  the  Reclamation  Service  the  general  outlines  of 
which  are  shown  in  Fig.  53.  The  valve  is  easily  operated  by  slight 
adjustment  of  the  pressure  in  the  cylinder  which  carries  the  conical 
plug  or  needle  point,  the  destructive  effect  of  the  escaping  water 
being  largely  neutrilized  by  this  form  of  orifice. 


FIG.  53. — Balanced  valve  for  regulating  reservoir  discharge  under  high  heads. 
Pathfinder  dam,  Wyoming. 


.  Fishways. — Where  diversion  dams  are  placed  in  perennial  streams, 
it  is  usually  required  by  state  law  that  some  form  of  fishway  or 
ladder  be  built  so  as  to  permit  the  fish  to  pass  the  obstruction. 
The  essential  features  are  an  inclined  way  on  the  slope  of  about 
one  in  four,  provided  with  compartments  making  a  series  of  boxes 


OUTLET  WORKS 


257 


258      PRINCIPLES  OF  IRRIGATION  ENGINEERING 

open  at  the  top.  From  the  top  down  each  is  successively  lower, 
the  water  flowing  from  the  higher  into  the  lower  down  this  slope. 

A  supply  of  water  of  at  least  5  cu.  ft.  per  second  is  usually  neces- 
sary to  operate  a  fish  ladder  of  this  character.  The  water  may  be 
allowed  to  spill  over  the  edges  from  one  box  or  compartment  to 
the  next  and  also  a  portion  may  flow  through  a  small  rectangular 
opening  in  the  lower  corner  of  each  compartment.  These  openings 
are  not  placed  in  line  with  each  other,  but  occupy  successive  alternate 
lower  corners  of  the  partitions,  so  that  the  water  entering  one 
compartment  seeks  the  lower  corner  where  it  escapes  through  the 
opening  usually  8  in.  high  by  12  in.  wide.  It  then  flows  diagonally 
across  the  next  compartment  to  the  lower  corner  and  so  on,  there 
being  formed  a  succession  of  pools  in  which  the  fish  can  rest,  and 
then  dart  through  the  submerged  opening  or  they  may  leap  over 
the  crest  into  the  next  pool  as  shown  in  Fig.  54. 

The  partitions  are  not  arranged  at  right  angles  to  the  slope  but 
are  inclined  so  that  the  water  flowing  through  them  will  wash  the 
sediment  into  the  lower  corner  and  out  into  the  next  compartment. 

For  a  dam  20  ft.  high,  the  runway  would  extend  80  ft.,  and  so  on. 
Care  must  be  taken  to  have  the  lower  end  of  the  fishway  brought 
into  the  pool  below  the  dam  and  into  water  where  the  fish  will 
readily  find  entrance. 

Spillway  Requirements. — A  spillway  consists  of  an  opening  or 
space  provided  in  or  at  the  side  of  a  hydraulic  structure,  such  as  a 
dam  or  canal,  and  in  such  position  that  when  the  water  rises  above  a 
certain  elevation,  it  will  escape  through  this  opening  into  a  channel 
from  which  it  can  be  delivered  usually  to  natural  drainage  line  and 
with  the  least  injury  or  inconvenience.  As  a  rule  some  form  of 
structure  must  be  provided  for  a  spillway,  although  in  rare  cases, 
conditions  may  be  utilized  in  such  way  as  to  permit  water  to  escape 
over  the  natural  rock  surface.  Even  in  this  case,  however,  it  is 
usually  necessary  to  trim  the  rock  and  provide  an  artificially  leveled 
lip  or  sill  over  which  the  water  may  flow. 

The  first  requirement  is  that  the  spillway  shall  have  ample 
length  and  capacity,  so  that  before  the  water  rises  above  the  desig- 
nated safe  level,  it  will  begin  to  escape  in  a  broad  thin  sheet,  and  not 
continue  to  rise  rapidly  to  a  height  which  will  endanger  the  works. 
Next  to  the  width  are  the  considerations  of  permanency  and  strength, 
as  a  spillway  may  be  called  upon  to  handle  large  volumes  of  water 
coming  quickly  during  the  time  of  extraordinary  rains,  causing 
floods. 


OUTLET  WORKS  259 

Spillway  Design. — The  design  of  any  form  of  spillway  is  largely 
controlled  by  the  surrounding  conditions,  more  perhaps  than  in 
many  other  structures  in  the  irrigation  system.  In  the  case  of  the 
storage  dam  the  spillway  location  must  be  governed  by  the  topo- 
graphy and  the  design  affected  by  the  natural  slopes  which  lead 
away  from  the  point  of  overflow.  Sometimes  it  is  almost  impossible 
to  find  a  suitable  point,  and  it  becomes  necessary  to  modify  the  shape 
of  the  dam,  lowering  a  part  of  the  crest  so  as  to  provide  a  spillway 
over  one  end,  as  for  example,  on  the  new  Croton  Dam  for  the  City 
of  New  York,  where  the  right-hand  end  of  the  dam  is  curved  up- 
stream practically  parallel  with  the  side  walls  and  prolonged  in  a 
low  lip  over  which  the  water  pours  into  a  broad  flume  cut  in  the 
rocky  side.  A  similar  principle  is  used  where  a  canal  leading  from 
the  reservoir  is  enlarged  at  its  upper  end,  as  in  the  case  of  the  Avalon 
Dam  on  the  Carlsbad  project,  New  Mexico.  This  permits  taking 
care  of  a  part  of  the  flood  water  by  discharging  it  from  behind  the 
dam  into  the  head  of  the  enlarged  canal.  It  is  there  allowed  to 
escape  by  overflowing  the  masonry  edge  of  the  canal  or  let  out 
through  large  valves  located  in  the  bottom  of  a  canal. 

It  is  also  desirable  in  some  instances  to  design  the  spillway  so  that 
it  can  be  provided  with  automatic  gates  or  flash  boards  arranged  that 
water  can  be  held  up  on  the  spillway  to  the  limit  of  safety.  When 
it  rises  above  a  certain  point,  the  gates  are  opened  automatically  or 
by  hand.  The  simplest  device  of  this  kind  is  to  build  a  small  broad 
bank  or  ridge  of  earth  on  top  of  the  concrete  or  masonry  spillway. 
This  for  a  time  will  hold  back  the  water  to  a  depth  of  say  2  or  3  ft., 
but  when  it  is  overtopped  the  earth  is  quickly  swept  away,  thus 
releasing  the  excess  water. 

Determination  of  Capacity. — The  tendency  in  designing  spillways 
is  to  make  them  too  small  and  in  estimating  the  capacity  required 
to  base  the  figures  upon  assumptions  as  to  the  usual  flood  condi- 
tions. It  should  be  remembered,  however,  that  during  the  life  of 
the  structure  or  during  the  coming  century,  there  will  occur  some 
one  or  more  extraordinary  combinations  of  rainfall  or  melting  of 
snow,  which  will  produce  floods,  exceeding  the  previously  known 
maximum.  It  is  to  provide  for  these  extraordinary  conditions  that 
the  spillway  must  be  designed.  For  example,  on  Cache  Creek, 
a  tributary  of  Sacramento  River  in  California,  the  observations  in- 
dicated a  maximum  flood  of  about  20,000  second-feet,  but  from 
various  indications  one  of  the  engineers  figured  out  a  possible, 
although  improbable  flood  during  earlier  years  reaching  60,000 


260      PRINCIPLES  OF  IRRIGATION  ENGINEERING 

second-feet.  This  figure  was  generally  regarded  as  almost  absurd, 
but  upon  the  basis  of  these  extreme  assumptions,  a  spillway  capac- 
ity of  60,000  second-feet  was  provided.  It  was  hardly  finished 
before  a  flood  occurred,  such  as  had  never  before  been  known, 
with  a  probable  maximum  of  65,000  second-feet.  Had  not  the 
spillway  been  built  of  a  size  which  was  laughed  at,  the  structure 
would  probably  have  been  swept  away.  The  lesson  to  be  enforced 
is  that  the  engineer  in  such  cases  must  be  prepared  for  criticism 
and  ridicule  by  less  well-informed  people  for  building  very  large 
and  somewhat  expensive  spillway  openings  for  structures,  espe- 
cially storage  dams  where  there  is  a  large  catchment  area  upon 
which  storms  may  occur. 

The  determination  of  the  size  of  the  spillway  must  be  based  upon 
a  knowledge  of  the  area  which  is  drained  and  upon  measurements  or 
estimates  of  floods  which  have  previously  occurred.  It  is  essential 
to  study  the  rainfall  records  and  the  combinations  of  flood  which 
may  arise  from  unusual  storms  occurring  over  one  or  another  part 
or  the  whole  of  the  catchment  area. 

If,  for  example,  the  annual  rainfall  is  15  in.  and  the  catchment  area 
consists  of  undulating  plains  and  foothills,  the  ordinary  discharge 
following  a  well-distributed  rain  may  be  practically  nothing  at  the 
point  of  storage.  Experience  has  shown,  however,  that  the  greater 
part  of  the  annual  rainfall  may  occur  in  a  few  days  and  6  or  7  in.  of 
rain  may  fall  during  one  of  these  so-called  cloud  bursts.  Where, 
under  ordinary  circumstances,  this  rain  would  be  distributed  through 
several  weeks  or  months  and  would  be  lost  daily  by  evaporation  and 
seepage,  it  now  is  brought  together  in  the  usually  dry  channels  and 
comes  rushing  down  to  the  point  of  storage,  creating  a  flood  which 
moves  large  boulders  and  overtops  works  which  have  stood  perhaps 
for  several  decades. 

It  is  necessary,  therefore,  to  assume  these  extreme  conditions  and 
provide  for  a  possible  runoff  of  say  50  per  cent,  of  the  storm  or  for  at 
least  2  or  3  in.  of  rainfall  over  the  area,  even  though  this  may  not 
occur  more  than  once  in  a  lifetime. 

Location  and  Type. — Wherever  practicable,  the  spillway  should  be 
located  away  from  the  dam  or  principal  structure  which  it  is  designed 
to  protect,  in  order  to  guard  against  any  backcutting  or  other  de- 
structive action  due  to  the  passage  of  a  great  volume  of  water  during 
a  short  period.  It  is  frequently  necessary,  however,  on  account 
of  the  topography  of  the  country  to  construct  the  spillways  as  part 
of  the  masonry  dam,  and  to  permit  the  waste  water  to  flow  into  the 


OUTLET  WORKS  261 

stream  channel  immediately  below  the  dam.  In  such  case  provision 
must  be  made  against  the  water  backing  up  against  the  lower 
toe  of  the  dam  and  by  its  gyratory  motion  undercutting  or  weak- 
ening the  foundations.  In  the  case  of  earth  dams.,  it  is  particularly 
important  to  place  the  spillway  upon  rock,  or  the  most  solid  portion 
of  the  undisturbed  ground  protecting  this  with  pavement  of  rock  or 
concrete  in  such  way  as  to  prevent  cutting. 

The  type  of  spillway  is  governed  by  the  topography  of  the  country. 
It  is  usually  possible  to  find  a  depression  in  the  rim  of  a  reservoir 
which  may  be  enlarged  or  modified  in  such  form  as  to  provide  a  lip 
or  sill  of  several  hundred  feet  in  length.  In  some  cases,  as  that  at  the 
Shoshone  Dam,  Wyoming,  where  the  works  are  in  a  narrow  canyon 
with  almost  vertical  walls,  it  has  been  necessary  to  provide  a  spillway 
discharging  through  a  tunnel  around  the  end  of  the  dam.  It  was  not 
considered  safe  to  allow  the  water  to  pour  over  the  top  of  this  struc- 
ture 327  ft.  high.  In  this  case,  a  large  funnel-shaped  opening  has 
been  provided  with  a  broad  curved  lip,  15  ft.  below  the  top  of  the  dam, 
the  water  pouring  over  this  lip  falls  into  a  depression  in  which  it  con- 
verges to  enter  the  tunnel  where  with  a  velocity  of  upward  of  20  ft. 
per  second  it  passes  through  the  opening  in  granite  walls  out  well 
below  the  toe  of  the  dam. 

Grades  and  Velocities. — In  every  spillway  device  the  object  is  to 
take  the  water  away  as  rapidly  as  possible,  consistent  with  safety, 
and  therefore  the  maximum  allowable  grades  should  be  provided,  so 
as  to  reduce  the  size  of  the  channel  to  be  made.  If  the  discharge  is 
over  a  granite  or  similar  hard  rock,  the  spillway  may  consist  of  a 
series  of  falls  or  rapids.  If  through  softer  materials  such  as  shale,  it 
may  be  necessary  to  line  the  channel  with  concrete  and  reduce  the 
grade  to  prevent  the  excessive  velocities  wearing  out  the  lining.  As 
a  rule,  the  large  spillways  are  only  called  into  use  once  or  twice  a  year, 
or  perhaps  only  once  in  a  decade,  and  then  for  only  a  few  hours  or 
days,  so  that  such  erosive  forces  are  not  indefinitely  continued.  It  is 
therefore,  practicable  to  take  larger  chances  on  erosion  than  would  be 
the  case  with  structures  in  continuous  use,  that  is  to  say,  after  a  large 
flood  there  will  usually  be  an  interval  of  months  of  even  years  during 
which  any  small  damages  may  be  repaired,  so  that  it  is  perfectly 
proper  to  assume  the  probability  of  small  injuries.  On  the  other 
hand,  it  is  extremely  dangerous  to  incur  any  risk  which  may  take 
place  during  a  large  flood,  creating  an  injury  sufficient  to  disturb  the 
structure  and  to  release  the  stored  water  behind  the  spillway. 

Protection  against  Erosion. — The  most  effective  protection  against 


262      PRINCIPLES  OF  IRRIGATION  ENGINEERING 

erosion  is  by  suitably  placed  masses  of  masonry  or  lining  of  concrete 
as  shown  on  Plate  XVI,  Figs.  C  and  D.  In  some  cases,  logs  or  tim- 
ber may  be  used  to  protect  the  softer  rocks  or  points  of  weakness, 
as  this  timber,  although  it  may  be  warped  by  the  sun,  will  afford 
enough  protection  during  the  short  duration  of  flood  to  prevent 
injurious  action. 

The  concrete  lining  of  a  spillway  section  may  be  dispensed  with 
in  part  by  building  a  series  of  drops  or  pools,  although  it  is  generally 
found  to  be  more  economical  to  line  an  inclined  chute  with  a  rela- 
tively thin  mass  of  concrete  than  to  attempt  to  concentrate  the  fall 
in  a  few  places  by  using  heavy  structures. 


CHAPTER  XVIII 
WATER  RIGHTS 

Definition. — A  water  right  may  be  described  as  the  ownership  or 
claim  which  has  been  sustained  by  the  courts  or  some  form  of  action 
by  suitable  state  officials  by  which  there  has  been  established  the 
right  to  the  use  of  a  certain  quantity  of  water.  This  is  usually 
limited  by  seasons  or  periods  of  the  year,  that  is  to  say,  the  right 
to  the  use  of  water  taken  from  the  common  stock,  is  limited  not 
only  in  quantity,  but  also  in  duration,  being  as  a  rule  confined  to  the 
crop-growing  season.  There  are,  however,  water  rights  out  of  the 
crop  season  which  may  be  utilized  for  purposes  of  storage  in  reser- 
voirs and  in  some  cases  the  claims  are  made  that  the  rights  are  to 
possession  of  a  continuous  flow  of  water  at  all  times,  irrespective 
of  the  season. 

The  term  water  right  is  often  used  loosely  to  imply  simply  the 
claim  to  the  right  to  use  water  and  not  to  the  actual  established 
right.  For  example,  it  may  be  said  that  a  certain  water  right  in- 
cludes the  entire  flow  of  a  given  stream,  meaning  by  this  that  the 
claim  is  made  that  the  entire  flow  belongs  to  or  is  appurtenant  to 
certain  described  tracts  of  land.  The  distinction  should  be  made, 
however,  between  the  actual  rights  as  properly  established  or  con- 
firmed and  those  which  are  more  or  less  vague  and  arising  simply 
from  notices  posted  or  entered  upon  the  county  or  state  records 
and  which  have  not  ripened  by  process  of  law  into  actual  rights. 

The  engineer  having  determined  from  the  physical  standpoint 
that  there  is  an  adequate  supply  of  water  for  the  proposed  irriga- 
tion works,  must  give  careful  consideration  to  the  question  as  to 
whether  the  rights  to  the  use  and  control  of  this  water  have  been  or 
can  be  properly  guarded.  Many  an  engineering  work  otherwise 
successful  has  been  a  failure  because  of  neglect  of  this  precaution, 
as,  for  example,  where  an  engineer  has  made  his  plans  with  reference 
to  the  given  volume  of  water  which  he  has  found  to  exist,  but,  to 
his  astonishment,  has  later  found  that  the  title  to  this  has  been  so 
insecure  that  his  works  have  never  been  able  to  operate  successfully. 

The  legal  and  engineering  questions  relating  to  water  rights 
merge  in  such  way  as  to  be  practically  inseparable.  This  is  because 

263 


264      PRINCIPLES  OF  IRRIGATION  ENGINEERING 

of  the  fact  that  water  occurring  in  nature  in  fluctuating  volumes  is 
not  susceptible  of  exact  limitation  by  metes  and  bounds,  as  is  real 
estate  and  it  is  not  possible  to  establish  accurate  lines  of  division  in 
the  same  way  that  farm  boundaries  can  be  laid  out  upon  the  ground. 
In  the  case  of  a  stream  which  on  one  day  is  carrying  300  second-feet 
and  on  another  30,000  second-feet,  and  on  which  the  claims  to  the 
water  at  the  various  points  along  its  course  may  aggregate  1,000 
second-feet,  the  problem  of  exact  limitation  of  the  quantity  avail- 
able to  each  of  several  hundred  claimants  is  a  mixture  of  physical 
and  legal  problems  which  can  be  solved  only  by  the  engineer  and 
lawyer  working  together,  each  having  a  fair  comprehension  of  the 
technical  requirements  of  the  other. 

The  proper  acquirement  of  the  rights  to  the  use  of  water  and  the 
perpetual  protection  of  these  are  among  the  most  vital  points  in 
the  planning  of  any  irrigation  project  or  system.  While  it  is  not  to 
be  supposed  that  the  engineer  or  businessman  having  to  do  with 
irrigation  works  is  fully  versed  in  the  details  of  irrigation  law,  yet 
it  is  necessary  that  he  have  such  knowledge  of  the  fundamental 
facts  and  sufficient  grasp  of  the  general  principles  to  be  reasonably 
certain  that  the  rights  involved  are  adequate.  At  least,  he  should 
have  such  general  knowledge  of  the  dangers  as  will  lead  him  to  call 
for  the  best  procurable  legal  advice  upon  the  points  involved. 

The  method  of  determination  of  the  rights  to  the  use  of  water 
and  the  operations  or  practices  are  by  no  means  uniform  nor  certain. 
The  whole  subject  of  water  law  as  pertaining  to  irrigation  is  still 
in  a  state  of  evolution  and  every  important  point  should  be  thor- 
oughly questioned  and  carefully  considered  in  advance  of  entering 
upon  any  new  scheme. 

There  is  great  apparent  contradiction  in  court  decisions  on 
fundamentals  and  their  application,  so  that  no  important  point  should 
be  assumed  as  established  until  thoroughly  examined  and  passed 
upon  by  competent  authorities. 

Origin  of  Water  Rights  in  the  United  States. — Water  rights  in  the 
arid  western  states  of  the  Union  are  derived  primarily  from  the 
original  federal  ownership  or  authority,  as  nearly  all  of  the  arid 
lands  formerly  belonged  to  the  United  States.  These  lands  have 
been  or  still  are  at  the  disposal  of  Congress  and  for  the  most  part  are 
open  to  settlement  under  the  homestead  laws.  With  the  ownership  of 
the  arid  land  was  included  also  the  ownership  of  the  waters  originat- 
ing in  the  mountains  or  elevated  plateaus  of  the  national  domain. 

One  of  the  conditions  attached  to  the  disposition  of  the  arid 


WATER  RIGHTS  265 

areas,  notably  under  the  terms  of  the  Desert  Land  Act,  is  to  the 
effect  that  they  must  be  reclaimed  by  the  use  of  waters  taken  from 
the  streams,  and  applied  to  the  soil,  the  water  thus  taken  not  being 
returned  to  the  water  course. 

This  requirement  of  taking  water  from  the  rivers  enacted  into 
law  by  Congress,  is  a  recognition  of  the  common  need  of  the  country 
of  the  diversion  of  the  streams  to  irrigate  the  arid  lands.  It  also 
illustrates  the  fact  that  the  riparian  ownership  of  water  as  embodied 
in  the  common  law  of  England  and  in  the  statutes  of  the  eastern 
states  is  not  applicable  to  the  needs  of  the  people  of  the  arid  regions. 

Under  the  theory  of  riparian  rights  each  owner  along  the  natural 
stream  enjoys  the  right  to  have  this  stream  flow  in  its  natural  state 
practically  undiminished  in  quantity,  and  unchanged  in  quality. 
This  is  in  accordance  with  the  common  necessities  of  a  humid  region 
where  there  is  usually  water  in  excess  and  where  no  one  man  should 
be  allowed  to  interfere  with  the  natural  behavior  of  the  stream  to  the 
detriment  of  his  neighbors. 

In  the  arid  region,  however,  this  "let  alone"  policy  is  obviously 
impracticable.  The  lands  cannot  be  put  to  their  best  uses  without 
taking  water  from  the  stream.  This  water,  if  put  to  beneficial  use, 
cannot  be  returned  to  the  stream,  and  hence  the  flow  of  rivers  must 
be  systematically  diminished  and  finally  the  beds  will  become  nearly 
if  not  quite  depleted  if  the  arid  region  is  to  be  reclaimed.  The  time 
is  rapidly  approaching  when  in  the  lower  courses  of  the  natural 
streams  there  should  be  no  water  left,  excepting  possibly  in  times  of 
unusual  floods.  If  water  is  thus  found,  it  may  be  considered  as  an 
indication  of  poor  management  or  imperfect  control  of  the  natural 
resources  of  the  area. 

The  generally  accepted  theory  that  water  in  a  natural  stream  is  the 
property  of  all  of  the  people  is  based  on  the  fundamental  fact  that 
it  is  essential  to  all  life,  both  animal  and  vegetal.  In  distinction 
to  natural  streams,  however,  are  the  waters  which  occur  in  springs 
or  wells  upon  certain  tracts  of  land  and  which  are  considered  as 
belonging  to  the  owner  of  that  particular  tract  of  land.  With  the 
proprietorship  in  springs  may  be  classed  also  certain  waters  taken 
from  a  natural  stream  and  put  in  an  artificial  reservoir.  When  thus 
severed  from  the  common  ownership  such  waters  become  the  prop- 
erty of  the  owner  of  this  reservoir,  and  are  no  longer  subject  to  the 
rules  governing  flowing  waters. 

In  some  of  the  western  states,  the  claim  is  occasionally  made 
that  the  natural  waters  belong  not  to  the  people  but  to  the  state 


266      PRINCIPLES  OF  IRRIGATION  ENGINEERING 

and  that  the  state  may  dispose  of  these  waters  in  accordance  with 
law.  But,  it  is  more  generally  held  that  the  control  of  the  state 
arises  not  through  actual  ownership,  but  through  other  powers. 
It  is  universally  recognized  that  the  state  must  have  such  direct 
control  over  the  distribution  of  the  waters  to  the  claimants  as  will 
insure  an  orderly  use  of  these  and  prevent  discord. 

As  there  is  not  sufficient  water  in  the  arid  region  for  all  purposes, 
the  great  question  next  to  that  of  ownership  is  as  to  who  shall 
take  from  the  common  stock  and  who  must  be  denied  the  water 
which  is  necessary  for  life  and  for  crop  production.  A  rule  generally 
recognized  is  that  of  first  in  time  is  first  in  right,  but  this  must 
again  be  modified  by  other  considerations,  as  the  first  man  who 
takes  the  water  may  desire  to  use  it  in  ways  not  wholly  in  accordance 
with  the  common  good.  Thus  have  arisen  the  superior  claims  for 
water  needed  for  the  sustenance  of  life,  that  is,  for  domestic  purposes, 
for  cattle,  and  for  municipalities  as  being  prior  to  all  others.  Next 
comes  agriculture,  or  the  needs  of  crops  produced  for  food  to  sustain 
life,  then  manufacturing  or  industrial  purposes,  as  less  important 
than  the  fundamentals  of  drink  and  food. 

Having  settled  that  priority  of  appropriation  and  use  shall 
govern  and  that  within  these  priorities  there  are  certain  superior 
needs,  the  next  broad  question  is  that  connected  with  considerations 
of  waste  of  water.  On  this  point,  the  most  generally  accepted 
rule  is  that  which  has  been  incorporated  in  the  Reclamation  or 
Newlands  Act  of  June  17,  1902,  which  states  "that  the  right  to 
the  use  of  water  acquired  under  the  provisions  of  this  act  shall  be 
appurtenant  to  the  land  irrigated  and  beneficial  use  shall  be  the 
basis,  the  measure,  and  the  limit  of  the  right."  This  embodies 
two  distinct  and  fundamental  ideas  vital  to  the  proper  use  of  the 
common  fund  of  water.  First,  of  appurtenance  to  the  lands  irri- 
gated, and  second,  of  beneficial  use. 

The  appurtenance  to  the  lands  irrigated  means  that  when  water 
has  been  appropriated  for  a  certain  tract  of  land,  the  water  needed 
for  this  land  goes  with  it  and  is  not  held  separately  in  a  way  such 
that  the  land  may  be  deprived  at  some  future  time  of  the  necessary 
supply.  The  importance  of  this  principle  is  not  dependent  wholly 
upon  the  need  of  the  particular  tract  of  land  under  consideration, 
but  is  in  recognition  of  the  fact  that  other  rights  grow  up  in  time 
such  that  if  water  is  not  used  upon  this  particular  piece  of  land, 
but  should  be  transferred  elsewhere,  confusion  would  ensue  with 
a  consequent  loss  directly  or  indirectly  to  other  lands. 


WATER  RIGHTS  267 

The  second  and  perhaps  more  important  rule  is  that  of  beneficial 
use.  Usually,  the  law  does  not  attempt  to  state  in  engineering 
terms  how  much  water  shall  be  used  on  any  tract  of  land,  but  limits 
this  by  the  broad  definition  of  beneficial  use.  At  first,  a  certain 
40-acre  tract  may  require  a  large  amount  of  water,  while  the  sub- 
soil is  being  filled  and  the  surface  subdued  or  filled  with  humus. 
At  a  later  time,  with  increase  of  irrigation  in  the  vicinity  and  with 
the  changes  which  follow,  a  very  small  amount  of  water  may  be 
applied  to  the  surface  and  sometimes  none  at  all  throughout  an 
entire  crop  season.  The  rule  of  beneficial  use  works  automatically 
in  that,  if  water  is  not  actually  needed  for  this  particular  tract, 
none  may  be  successfully  claimed. 

Riparian  Rights. — Under  the  term  riparian  rights  are  included 
those  claims  to  adjacent  waters  established  by  usage  or  by  judicial 
processes  under  which  the  owners  of  land  adjoining  a  stream  enjoyed 
the  direct  or  indirect  use  of  these  waters.  These  riparian  rights  are 
generally  limited  in  such  way  that  the  abutting  landowner  may  take 
some  of  the  water  for  domestic  use  or  for  cattle  or  for  manufacturing 
and  other  industrial  purposes  but  his  rights  are  limited  by  those  of 
the  entire  community.  These  usually  require  that  the  water  be  left 
practically  undiminished  in  quantity  and  unpolluted  or  otherwise 
changed  in  quality. 

The  doctrine  of  appropriation  and  priority  of  use  has  been  gen- 
erally adopted  throughout  the  arid  part  of  the  United  States.  This 
is  in  direct  opposition  to  the  principles  governing  flowing  water  which 
are  embodied  in  the  laws  and  court  decisions  of  the  eastern  or  humid 
states.  Within  these  the  so-called  riparian  rights  prevail,  being 
adopted  from  English  practice. 

Riparian  rights  are  founded  upon  the  theory  that  there  is  enough 
water  for  every  ordinary  purpose  and  to  spare,  and  that  the  flowing 
water  cannot  be  diverted  to  the  exclusive  use  of  any  one,  excepting  as 
far  as  ownership  of  the  lands  along  the  banks  may  permit  such  di- 
versions. Each  landed  appropriator  bordering  upon  a  stream  must 
permit  the  flow  to  continue  practically  undiminished  in  quantity 
and  quality.  He  may  take  it  out  upon  his  own  land,  but  he  must 
return  it  after  having  put  the  water  to  use  for  power,  or  for  other 
purposes.  The  enforcement  of  any  such  doctrine  is,  of  course, 
directly  antagonistic  to  the  common  needs  of  the  people  of  the  arid 
region  where  the  lands  have  little  if  any  value  excepting  by  the  use  of 
the  water  taken  from  the  streams. 

The  riparian  law  was  founded  upon  the  common  needs  of  the  people 


268      PRINCIPLES  OF  IRRIGATION  ENGINEERING 

of  a  humid  region.  It  was  the  outgrowth  of  practical  or  common 
sense  as  applied  to  the  daily  problems.  In  England  it  has  been 
modified  from  time  to  time  according  to  the  conditions  of  develop- 
ment of  the  country  and  the  larger  needs  of  the  people  but  in  the 
humid  parts  of  the  United  States,  the  riparian  doctrine  has  become  so 
crystallized  into  law  and  so  rigid  in  application  that  to  a  large  extent 
it  has  not  been  conducive  to  the  largest  possible  development  of 
water. 

In  the  arid  regions  the  riparian  rules  are  not  wholly  applicable,  as 
there  the  common  needs  of  the  people  are  dependent  upon  taking 
water  away  from  the  stream,  using  it  and  returning  little,  if  any,  to 
the  natural  drainage.  On  the  extreme  western  border  in  California, 
a  state  partly  humid,  the  system  of  laws  originally  adopted  by  the 
Americans  were  copied  from  those  of  the  eastern  humid  states  and 
included  the  ideas  of  riparian  rights.  In  the  arid  portion  of  the  state, 
however,  especially  near  the  old  Missions,  there  grew  up  in  accord- 
ance with  the  needs  of  the  people,  the  recognition  of  the  Spanish 
theory  of  appropriation  and  use  of  waters.  Thus  these  two  antago- 
nistic principles  came  into  conflict  as  the  state  was  developed. 

The  result  has  been  innumerable  controversies  and  court  decisions 
which  at  one  time  appear  to  favor  riparian  rights,  and  at  another 
the  necessary  rules  of  appropriation.  Neither  has  yet  been  definitely 
and  conclusively  established  as  against  the  other,  but  there  appears  to 
be  a  tendency  to  interpret  the  riparian  rights  in  accordance  with 
beneficial  use,  that  is  to  say,  if  a  riparian  appropirator  has  put  the 
water  of  a  stream  to  beneficial  use  either  for  watering  his  cattle  or  for 
irrigating  his  land,  he  will  be  protected  in  this,  but  he  may  not  neg- 
lect to  use  the  water  indefinitely  and  then  at  some  future  time  demand 
his  riparian  rights  to  the  destruction  of  valuable  improvements  and 
irrigated  lands  above  or  below  him. 

It  is  essential  that  the  engineer  in  planning  his  works  know  some- 
thing of  the  extent  of  the  riparian  rights  which  may  be  claimed  upon 
the  streams.  He  should  receive  definite  assurance  that  such  rights 
do  not  exist,  or  are  limited  and  that  he  may  depend  upon  the  rules 
of  appropriation  for  the  water  supply  needed  for  success. 

Acquisition  of  Water  Rights. — Starting  with  the  proposition  that 
the  Federal  Government  permits  and  requires  the  diversion  of  streams 
on  the  public  domain  for  reclaiming  desert  lands,  as  a  requisite  to 
obtaining  title  to  these,  it  has  followed  that  as  new  states  are  created 
within  the  arid  regions  and  duties  of  providing  systematic  methods 
of  administration  are  prescribed,  these  newer  states  of  necessity 


WATER  RIGHTS  269 

have  been  forced  to  consider  the  orderly  distribution  of  the  waters 
and  the  adoption  of  certain  broad  fundamental  rules.  As  previously 
noted,  in  most  of  the  state  constitutions  of  the  arid  region,  it  is 
recognized  that  the  waters  belong  to  the  people.  In  some  of  the 
states  the  phrase  is  used  in  such  a  sense  as  to  imply  that  they  belong 
to  the  state  but  this  ownership  by  the  state  is  obviously  not  the  char- 
acter of  ownership  by  which  the  state  may  sell  or  dispose  of  these 
waters  or  deal  in  them  as  it  might  in  lands  or  buildings. 

Assuming  as  true,  the  fundamental  proposition  that  the  waters 
belong  to  the  people,  next  comes  the  recognition  of  the  fact  that  as 
there  is  not  enough  water  for  all  of  the  people  and  there  must  be 
some  orderly  system  for  distributing  these  and  for  giving  to  certain 
persons  an  exclusive  right  or  an  artificial  monopoly.  This  is  gener- 
ally done  in  accordance  with  the  rule  that  a  man  first  in  time  is 
first  in  right.  If  the  first-comer  should  claim  everything  in  sight 
there  will  be  nothing  left  for  the  next  man.  It  follows  that  it  is  neces- 
sary to  modify  this  rule  by  another,  namely,  that  the  man  first  in 
time  shall  be  limited  to  an  amount  of  water  which  he  put  to  beneficial 
use.  Otherwise,  he  might  file  claims,  as  many  pioneers  have  done, 
to  the  entire  flow  of  the  river,  proceed  to  divert  a  small  percentage 
of  it  and  try  to  hold  the  rest  for  speculation  profit. 

In  determining  officially  the  amount  to  which  each  claimant  is 
entitled,  it  is  necessary  for  him  to  show  that  he  put  the  water  to 
beneficial  use  to  a  certain  extent  prior  to  a  certain  date,  or  to  the 
time  when  others  also  utilized  portions  of  the  water.  This  is  em- 
bodied as  before  pointed  out  in  the  latter  part  of  the  provision  in 
the  Reclamation  Act  to  the  effect  that  "  the  right  to  the  use  of  water 
shall  be  appurtenant  to  the  land  irrigated,  and  beneficial  use  shall 
be  the  basis,  the  measure,  and  the  limit  of  the  right." 

The  methods  of  acquiring  water  rights  are  variable;  each  of  the 
states  has  its  own  system  or  lack  of  system  in  the  matter.  In  general, 
it  may  be  said  that  all  of  the  states  recognize  rights  as  acquired  by 
actual  construction  of  works  and  by  the  application  of  the  water 
to  the  land  or  by  exercising  due  diligence  in  making  such  applica- 
tion of  the  water.  In  some  of  the  states  a  regular  system  is  provided, 
namely,  of  applying  to  a  state  official.,  usually  the  state  engineer, 
for  permission  to  divert  a  certain  stated  amount  of  water  for  irri- 
gation for  a  definite  tract  of  land.  It  is  supposed  to  be  the  duty  of 
this  official  to  ascertain  whether  there  is  actually  water  available 
for  appropriation.  To  do  this  he  takes  i  into  consideration  what  is 
known  of  the  flow  of  the  stream  and  of  the  appropriations  already 


270      PRINCIPLES  OF  IRRIGATION  ENGINEERING 

made.  If  he  is  satisfied  that  there  is  water  which  as  yet  has  not  been 
appropriated,  a  permit  is  issued.  If  work  is  pursued  with  diligence 
and  proof  is  made  of  actual  reclamation,  the  right  then  becomes 
established. 

In  case  of  shortage  the  prior  appropriators  receive  their  full  supply, 
and  the  later  appropriators  receive  what  is  left,  each  in  the  order  of 
the  date  of  the  official  records. 

In  other  states,  where  an  orderly  or  business-like  system  has  not 
been  developed,  it  is  customary  to  post  notices  of  appropriation 
along  a  stream  or  at  the  point  of  proposed  diversion  of  the  water,  and 
to  make  this  notice  a  matter  of  record  within  the  county.  Thus,  as 
developments  proceed  to  a  point  where  there  is  scarcity  of  water  and 
controversies  arise,  it  is  necessary  to  bring  the  whole  matter  into 
court,  and  to  settle  relative  rights  according  to  the  testimony  of  the 
older  inhabitants. 

This  has  proved  an  expensive  and  dilatory  process  and  in  some 
counties  it  has  been  asserted  that  the  expenses  of  litigation  are  greater 
than  those  of  construction.  For  example,  "A"  may  bring  suit 
against "  B  "  to  settle  their  relative  priorities,  and  "  B  "  against  "  C," 
and  so  on,  with  infinite  combinations,  and  when  all  have  been  ex- 
hausted some  successors  to  older  and  apparently  abandond  claims 
X,  Y,  or  Z,  may  bring  suits  individually  or  against  collective 
groups,  and  get  the  whole  matter  again  into  court.  Wherever 
practicable,  the  attempt  is  now  made  to  include  in  one  suit  all  of 
the  possible  claims  on  the  river  and  its  tributaries,  and  in  some  in- 
stances in  order  to  settle  relative  rights,  suit  has  been  brought  against 
upward  of  4,000  individuals. 

The  recognition  of  the  necessity  of  an  orderly  and  systematic 
procedure  in  establishing  rights  to  the  use  of  water  has  not  yet 
reached  the  point  of  completeness  in  the  United  States  comparable 
to  that  attained  with  reference  to  land  titles.  While  great  care  is 
exercised  in  verifying  every  point  with  reference  to  title  to  a  farm, 
there  still  exists  a  relatively  chaotic  condition  with  reference  to  the 
water  which  in  many  localities  alone  gives  value  to  this  land.  We 
are  still  in  many  parts  of  the  country  in  what  may  be  called  a  medie- 
val condition  as  regards  titles  to  water,  one  where  each  man  claims 
everything  in  sight  and  the  aggregate  of  the  claims  exceeds  by  many 
times  the  amount  of  water  available.  With  the  rapid  development 
of  a  higher  standard  of  public  or  civic  morals  must  come  the  recogni- 
tion of  the  necessity  of  simple  and  comprehensive  methods  of  secur- 
ing titles  to  the  .use  of  the  flowing  waters. 


WATER  RIGHTS  271 

While  there  is  great  uncertainty  in  these  matters,  and  caution 
must  be  used,  yet  this  uncertainty  is  not  such  as  should  deter  legiti- 
mate investment,  for  it  has  been  shown  that  good  faith  in  the  con- 
struction of  works  which  are  adequate  to  hold  and  distribute  the 
water  supply,  followed  by  continuous  beneficial  application  has 
usually  been  sufficient  to  constitute  an  appropriation  which  will  be 
sustained  in  legal  controversies.  In  the  majority  of  the  cases  where 
water  is  available  and  men  have  proceeded  in  good  faith  to  utilize 
it,  and  have  done  so,  the  probability  is  that  they  may  continue  in  this 
without  molestation. 

Theory  Upon  Which  Granted. — As  stated  in  previous  para- 
graphs, the  theory  upon  which  the  right  to  the  use  of  water  is 
granted  by  the  state  or  confirmed  by  the  courts  is  that  of  beneficial 
use  in  the  order  of  priority  of  appropriation,  or  of  time  in  which 
this  has  been  put  to  such  beneficial  use.  The  man  who  first  builds 
a  canal  from  a  stream  and  utilizes  it  is  almost  invariably  pro- 
tected in  such  use  and  to  the  extent  to  which  he  has  beneficially 
applied  it,  as  against  all  subsequent  appropriators,  especially  if  he 
has  endeavored  to  make  record  of  this  fact  in  the  proper  place  with 
the  county  or  state  authorities. 

On  nearly  every  stream  notices  have  been  posted  at  various 
points  claiming  a  thousand  miner's  inches  or  any  other  large  quan- 
tity. The  amount  claimed  is  usually  some  figure  or  phrase  which 
appeals  to  the  fancy  of  the  would-be  appropriator  rather  than 
applicable  to  the  physical  facts.  Relatively  few  of  these  early 
claimants  had  any  conception  as  to  what  was  the  volume  of  a  miner's 
inch  or  of  a  cubic-foot  per  second,  hence  their  filings  have  been 
for  a  volume  sometimes  exceeding  that  of  the  stream,  or  even  by 
mistake  for  an  amount  so  small  as  to  be  insignificant.  Adding 
these  claims,  the  total  is  sometimes  ten  times  that  of  the  flood  flow. 
In  attempting  to  apply  these  claims,  however,  the  basis  of  recogni- 
tion of  appropriation  has  been  not  as  to  the  quantity  which  has 
been  claimed  but  upon  the  amount  which  has  been  or  is  actually 
being  used,  as  shown  by  the  size  of  the  canal  and  the  number  of 
acres  irrigated. 

For  example,  the  early  appropriator  in  his  ignorance  of  quantities 
of  waters  may  have  filed  upon  10,000  miner's  inches,  or  200  second- 
feet.  His  canal  as  first  constructed  may  have  carried  10  second- 
feet  and  may  have  been  enlarged  to  20  second-feet.  If  he  has  shown 
due  diligence  in  this  enlargement  it  is  probable  that  when  the  matter 
comes  to  final  determination,  he  may  be  given  a  priority  of  20 


272      PRINCIPLES  OF  IRRIGATION  ENGINEERING 

second-feet,  dating  from  his  original  notice,  or  he  may  be  awarded 
10  second-feet,  as  a  first  priority,  and  an  additional  10  second-feet 
to  cover  the  enlargement,  this  later  amount  being  subsequent  to 
the  claims  of  some  other  appropriator.  If  there  are,  say,  100  such 
appropriators  along  a  stream,  and  each  has  made  enlargements 
at  different  times,  it  is  easy  to  see  how  complicated  the  official 
adjudication  of  water  must  be  where  the  fact  must  be  established 
as  to  the  relative  dates  at  which  each  important  enlargement  of 
the  various  canals  has  been  made. 

Beneficial  Use  of  Water. — The  principal  fact  to  be  established 
beyond  the  date  of  original  appropriation  and  construction  is  the 
fact  that  the  water  has  been  put  to  beneficial  use.  The  mere  state- 
ment that  the  original  claim  was  initiated  at  a  given  time  has  rela- 
tively little  force  as  any  one  may  have  claimed  the  waters  of  an 
entire  river  by  simply  posting  notices  to  this  effect.  The  vital  test 
must  be  as  to  whether  the  claimant  actually  took  the  water  from 
the  stream  and  used  it  beneficially,  not  wasting  it  nor  trying  to  hold 
it  for  speculative  purposes. 

Unless  the  test  of  beneficial  use  is  applied,  it  is  easy  to  create  a 
monopoly  of  this  great  necessity  of  life.  A  man  might  lay  claim 
to  the  waters  of  many  streams  and  in  this  way,  although  owning 
little,  if  any,  land,  be  able  to  levy  tribute  upon  every  industry  and 
even  upon  life  itself  within  the  district.  Such  condition  is  repugnant 
to  public  welfare  and  hence  there  has  arisen  naturally  the  simple 
rule  that  each  claimant  must  prove  beneficial  use  and,  having  made 
proof,  he  should  be  protected  in  the  continued  use  until  abandon- 
ment of  it  has  been  shown. 

Beneficial  use  of  water  for  irrigation  may  be  defined  as  such 
application  of  the  water  as  will  result  in  prolongation  of  life,  animal 
or  vegetal,  and  in  the  increased  value  of  crops  or  in  the  production 
of  power  necessary  in  various  industries.  While  any  general 
definition  is  necessarily  vague,  yet  in  each  specific  case  it  is  usually 
easy  to  determine  whether  the  water  has  been  put  to  beneficial 
use  by  an  examination  of  the  facts.  It  is  peculiarly  the  duty  of 
the  engineer  in  connection  with  those  of  the  lawyer,  in  considering 
the  relative  rights  to  water,  to  make  the  measurements  and  deduc- 
tions which  establish  the  actual  facts.  For  example,  a  canal  con- 
structed to  carry  100  second-feet  and  taking  water  to  1,000 
acres  cannot  be  considered  to  have  a  proper  claim  to  its  entire 
capacity  for  beneficial  use,  as  this  amount  of  water  should  be  suffi- 
cient for  10,000  acres. 


WATER  RIGHTS  273 

On  the  other  hand,  a  canal  of  10  second-feet  capacity  which  is 
claimed  to  irrigate  10,000  acres  cannot  form  the  basis  for  a  claim  to 
sufficient  water  for  this  10,000  acres  because  it  is  obvious  that  the 
water  could  not  be  delivered  through  such  a  canal,  its  capacity  being 
entirely  too  small.  Thus,  the  determination  of  beneficial  use  in  any 
particular  case  or  groups  of  cases  is  one  of  fact  which  can  be  deter- 
mined only  upon  the  ground  and  established  by  the  testimony  of 
competent  men. 

Water  Rights  Apart  from  Lands. — Under  the  theory  which  is 
generally  accepted  as  correct  throughout  the  greater  part  of  the  arid 
region,  there  cannot  be  nor  should  there  be  any  such  thing  as  right  to 
flowing  water  independent  of  ownership  of  certain  tracts  of  land. 
In  other  words,  public  policy  demands  that  each  water  right  shall  be 
appurtenant  to  a  certain  specific  tract  of  land  upon  which  the  water 
may  be  put  to  beneficial  use.  Unfortunately,  however,  there  has 
grown  up  in  some  of  the  states  and  been  recognized  by  the  courts  a 
theory  that  the  right  to  the  use  of  water  may  be  of  the  nature  of  per- 
sonal property  transferable  from  one  locality  to  another,  that  is  to  say 
a  man  may  own  in  a  certain  stream  enough  water  to  irrigate  100  acres. 
He  may  rent  this  to  a  neighbor  one  year  and  take  it  away  and  rent  it 
to  another  for  the  next  year.  The  objection  to  this  is  that  such 
ownership  is  not  consistent  with  the  public  welfare.  It  enables 
the  establishment  of  a  landlordism,  repugnant  to  the  popular  insti- 
tutions, as  it  enables  one  man  to  absolutely  control  the  source  of  life 
for  a  large  district. 

To  illustrate  this  point,  may  be  taken  the  extreme  case  where  in 
medieval  times  certain  authorities  claimed  the  exclusive  right  to  the 
air  over  certain  districts  and  endeavored  to  enforce  taxes  or  tribute 
upon  the  use  of  the  air! 

The  idea  of  ownership  of  water  apart  from  the  land  has  grown  up 
through  ownership  in  the  shares  of  stock  of  a  partnership,  cooperative 
agreement,  or  corporation,  which  has  built  a  system  of  irrigation. 
For  example,  a  half  dozen  farmers  owning  certain  lands  agree  among 
themselves  to  build  a  canal  to  irrigate  these  lands.  They  do  not  have 
sufficient  cash  capital  and  must  purchase  materials  or  hire  additional 
help,  so  a  capitalist  joins  with  them  with  the  understanding  that  he 
shall  own  a  proportional  part  of  the  carrying  capacity  of  the  canal. 
Thus,  the  farmers  obtain  the  waters  for  their  own  lands  or  for  a  part 
of  them  and  from  year  to  year  rent  from  their  associate  who  has  furn- 
ished the  capital,  the  use  of  the  additional  capacity  of  the  canal. 

This  is  a  proper  and  legitimate  conception  as  far  as  the  use  of  the 

18 


274      PRINCIPLES  OF  IRRIGATION  ENGINEERING 

canal  is  concerned,  but  it  is  easy  to  pass  from  this  rental  of  the  use  of 
the  canal  to  the  assumption  of  the  ownership  of  the  water  which  is 
taken  into  the  canal.  A  careful  distinction  should  be  drawn  between 
these  two.  It  may  be  possible  and  proper  to  recognize  that  the  water 
in  the  canal  is  appurtenant  to  the  tracts  upon  which  it  is  used.  The 
persons  owning  this  land  may  be  required  to  pay  a  tax  or  license  for 
the  transportation  of  the  water  by  means  of  the  canal  to  the  lands  to 
which  the  waters  are  appurtenant.  This  is  far  different  in  outcome  to 
the  proposition  that  the  water  is  owned  by  the  proprietors  of  the 
canal  which  transports  it.  As  before  stated,  this  claim  of  ownership 
of  the  water  by  the  canal  owners  has  been  recognized  in  some  states, 
but  the  tendency  is  to  acknowledge  the  right  to  carriage  only  and 
the  right  to  collect  dues  as  by  a  common  carrier  but  not  as  a  right  of 
ownership  of  the  flowing  water  apart  from  the  land. 


CHAPTER  XIX 
ECONOMIC  FEATURES  OF  IRRIGATION 

Feasibility  of  Irrigation. — After  all  of  the  detailed  studies  and 
examinations  have  been  made  of  the  engineering,  legal  and  related 
features  of  any  proposed  enterprise,  then  it  becomes  necessary  to 
study  the  whole  project  from  the  broad  standpoint  of  its  feasibility. 
It  is  assumed  as  a  matter  of  course  that  before  starting  any  detailed 
investigation,  its  feasibility  is  known  to  be  more  than  probable.  As 
a  result  of  careful  studies,  this  question  of  feasibility  must  be  prac- 
tically determined  before  entering  upon  expensive  construction. 

The  prime  consideration  as  regards  feasibility  is  based  upon  the 
probable  financial  outcome.  In  other  words,  will  the  enterprise  pay? 
This  is  true  not  only  from  the  individual  or  corporate  standpoint, 
but  also  from  that  of  the  state  or  nation.  The  financial  reward 
in  the  two  cases  may  be  estimated  on  a  different  basis,  that  is  to 
say,  the  individual  or  corporation  considers  the  financial  aspect  with 
reference  to  direct  profits  to  be  attained,  while  the  state  may  con- 
sider indirect  sources  of  profit  that  resulting  from  a  prosperous  tax- 
paying  citizenship. 

In  either  instance,  the  consideration  of  feasibility  can  best  be 
reduced  to  the  easily  understood  expressions  of  dollars  and  cents. 
This  is  the  measuring  stick  which  must  ultimately  be  applied  to  all 
proposed  enterprises. 

In  turn,  the  question  of  financial  profit  rests  upon  an  infinite 
variety  of  conditions  such  as  have  been  touched  upon  in  the  preced- 
ing pages.  These  may  be  grouped  under  the  two  general  headings 
of,  first,  physical  difficulties,  and,  second,  obstacles  of  human  origin. 
The  first  lie  directly  within  the  cognizance  of  the  engineer,  the  second, 
and  the  far  more  important  and  difficult,  lie  only  partly  within  his 
technical  skill,  the  remainder  being  largely  within  the  domain  of  the 
lawyer  or  specialist  in  various  lines. 

Fundamental  Questions  to  be  Considered. — Of  the  physical 
questions  to  be  answered,  the  first  and  most  important  is  usually 
that  of  water  supply.  Throughout  the  arid  region  as  a  rule,  there 
is  more  good  land  than  there  is  water,  and  the  chief  limitations  as 
before  stated  rest  upon  facts  as  to  whether  sufficient  water  can  be 

275 


276      PRINCIPLES  OF  IRRIGATION  ENGINEERING 

had  each  year  to  cover  a  given  area  of  land.  This  matter  being 
determined,  the  next  in  order  is  as  to  the  extent  and  character  of  the 
land,  and  its  location  with  reference  to  the  water  supply.  The 
quality  of  the  water  should  also  be  given  thought  as  in  many  parts 
of  the  west,  especially  during  low  water,  the  streams  carry  a  very 
large  amount  of  earthy  salts  in  solution,  and  i  n  times  of  flood,  great 
quantities  of  silt,  which  tends  to  choke  the  canals. 

The  human  obstacles  to  which  reference  has  been  made  are  those 
surrounding  the  control  of  the  water,  or  protection  of  the  rights  to 
the  continued  use  of  the  flowing  streams,  also  those  growing  out  of 
questions  of  rights  of  way  for  structures  and  of  the  relation  of  the 
management  of  the  canal  system  to  the  irrigators  upon  whose 
success  as  farmers  depends  the  ultimate  outcome  of  the  investment. 

Value  of  Land. — The  profits  to  be  made  from  any  irrigation 
development  lie  not  in  sale  of  the  water  but  in  the  increased  value 
of  the  lands  which  are  served.  This  simple  fact  has  frequently  been 
overlooked  and  as  a  result  many  irrigation  investments  have  been 
financial  failures.  There  has  been  too  much  dependence  upon  the 
assumed  profits  to  be  made  out  of  the  sale  of  water  rights  or  out  of 
the  operation  of  water  supply  system,  but,  as  a  matter  of  fact,  it 
has  been  found  that  the  only  profits  derived  are  those  from  the  in- 
creased value  of  the  land.  Assuming  that  the  soil  is  adapted  for 
agriculture,  as  it  is  throughout  the  greater  part  of  the  arid  region, 
the  lands  without  water  may  be  considered  as  having  little  or  no 
value  in  their  native  state,  hardly  more  than  the  cost  of  conveyanc- 
ing. With  water  they  have  a  large  potential  value,  or  will  pay  a 
large  rate  of  interest  when  developed,  upon  an  investment  of  $100 
to  $500  or  more  per  acre.  The  cost  of  bringing  water  to  these  lands 
may  be  assumed  to  be  $40  an  acre  and  the  increase  in  land  values 
may  be  several  times  this  cost  of  providing  water. 

This  gain  in  value  of  land  from  nothing  to  $100  an  acre  or  more 
goes  not  to  the  builders  of  the  canal  system,  but  to  the  owners  of  the 
land.  If  these  are  the  same  persons,  then  the  investment  may  be  a 
financial  success,  but  if  one  set  of  men  build  the  works  and  another 
set  own  the  land,  the  profits,  whatever  they  may  be,  almost  in  variably 
go  to  the  landowners.  The  investors  in  the  irrigation  works  as 
distinguished  from  landowners  as  shown  by  past  history,  have  al- 
most without  exception  lost  their  investment.  It  is  not  necessary 
at  this  time  to  trace  out  the  reasons  why  this  has  occurred,  but  as 
a  historic  fact,  this  may  be  stated.  The  men  who  have  put  their 
money  and  time  into  the  construction  of  irrigation  works  have  been 


ECONOMIC  FEATURES  OF  IRRIGATION  277 

" involuntary  philanthropists"  in  that  they  have  developed  a  coun- 
try and  made  possible  the  creation  of  wealth  for  others,  but  have 
not  been  able  to  bring  to  themselves  a  fair  share  of  the  reward. 

Increase  in  Value. — The  moment  that  an  irrigation  system  is 
projected,  there  attaches  to  the  land  which  may  be  covered  a  specu- 
lative value  and  the  selling  price  may  jump  from  the  government 
rate  of  $1.25  per  acre  up  to  $5  or  $10  per  acre,  on  the  assumption 
of  early  construction  of  the  project.  As  the  works  advance,  this 
speculative  value  becomes  more  and  more  inflated,  until  the  time 
arrives  when  it  becomes  necessary  for  the  owners  of  the  land  to 
begin  to  repay  a  part  of  the  money  invested  in  the  irrigation  works. 
Then  there  is  usually  a  sharp  decline  in  land  prices.  This  is  because 
of  the  realization  of  the  fact  that  payments  must  be  met  and  also  a 
better  appreciation  of  the  pioneer  conditions,  namely,  that  a  con- 
siderable amount  of  labor  and  money  must  be  invested  in  subduing 
the  soil  to  get  it  into  good  productive  capacity,  or  tilth. 

In  the  more  northern  states  where  the  crop  season  is  limited  to  the 
summer  months  and  where  two  or  possibly  three  cuttings  of  alfalfa 
can  be  had,  the  lands  as  they  are  brought  to  a  condition  of  tilth 
steadily  increase  in  selling  price.  This  may  go  up  to  $100  to  $150  per 
acre,  dependent  upon  the  degree  of  care  shown  in  levelling  the  fields 
for  irrigation  and  in  fertilizing  the  soil  to  bring  it  into  the  best 
agricultural  condition. 

There  is  a  common  fallacy  in  the  statement  that  the  soils  of  the 
arid  region  do  not  require  enrichment,  but  that  the  irrigation  water 
supplies  all  needs.  This  is  far  from  true,  for,  although  the  desert 
soils  frequently  contain  earthy  salts  of  value  to  plant  life  they  are 
usually  deficient  in  nitrogen  and  frequently  in  phosphates.  The 
nitrogen  can  be  supplied  by  cultivating  alfalfa,  clover,  or  plants  of 
related  families,  occasionally  turning  the  green  plants  under  by 
plow,  so  as  to  put  the  organic  matter  into  the  soil,  but  the  phosphates, 
if  needed,  must  be  brought  in  from  other  areas. 

In  the  more  southern  region,  with  warmer  climates,  especially 
where  fruits  can  be  grown,  or  where  the  number  of  cuttings  of 
alfalfa  may  be  increased,  the  land  values  are  correspondingly 
larger.  When  the  ground  has  been  properly  tilled  and  young 
orchards  set  out,  the  values  reach  into  hundreds  of  dollars  per  acre. 
Much  of  this  value  is  given  by  the  labor  which  has  been  spent  upon 
the  farm,  but  a  considerable  portion  is  what  may  be  called  the  un- 
earned increment  of  value,  due  to  the  bringing  in  of  the  water. 

This  increase  in  land  value  is  several  times  the  first  cost  of  the 


278      PRINCIPLES  OF  IRRIGATION  ENGINEERING 

water,  because  of  the  fact  that  the  control  of  the  water  is  practically 
a  monopoly,  there  being  usually  not  enough  water  for  all  of  the  good 
lands.  The  profits  to  be  obtained  are  thus  those  which  attach  to  the 
creation  of  a  monopoly,  and  these  come,  as  before  stated,  not  to  the 
builders  and  owners  of  the  canal  system,  which  transports  the  water, 
but  to  the  owners  of  the  land  to  which  the  water  must  neces- 
sarily be  appurtenant.  The  failure  to  recognize  this  simple  but 
fundamental  fact  has  led  to  many  failures  in  financing  irrigation 
enterprises. 

Soil,  Climate,  and  Crops. — In  all  considerations  of  reclamation 
schemes  due  attention  should  be  given  to  the  character  of  soil, 
to  the  climatic  conditions,  and  to  the  possibility  of  producing 
certain  classes  of  valuable  crops.  It  is  true  that  these  matters 
are  of  less  immediate  importance  than  those  of  water  supply,  because 
of  the  fact  that  taking  the  arid  region  as- a  whole,  the  soil  is  usually 
well  adapted  to  agriculture  and  the  climatic  conditions  are  generally 
favorable  to  the  production  of  some  kind  of  crop,  but  because  these 
matters  are  secondary  they  should  not  be  overlooked. 

Most  of  the  soils,  especially  of  the  desert  areas  are  somewhat 
sandy,  light,  and  easily  tilled.  In  the  lower  valleys,  however, 
there  are  frequently  large  areas  of  clay  or  adobe  which  require 
much  more  careful  manipulation  for  success.  Each  class  of  soil 
presents  its  peculiar  conditions  and  problems  and  requires  intelli- 
gently directed  efforts. 

Fortunately,  there  have  been  established  throughout  the  arid 
regions  experimental  stations  where  careful  observations  have  been 
and  are  being  made  as  to  the  results  of  different  methods  of  treat- 
ment and  the  agricultural  colleges  are  diffusing  information  as  to 
peculiar  conditions  to  be  met.  A  book,  or  in  fact  many  volumes, 
might  properly  be  devoted  to  the  subject  of  soils  in  their  relation  to 
irrigation,  but  it  is  sufficient  in  the  present  connection  to  call  atten- 
tion to  this  fact,  and  to  the  necessity  of  having  an  expert  examination 
of  the  soils  which  it  is  proposed  to  irrigate,  in  order  to  determine 
in  a  broad  way  the  fundamental  questions  as  to  the  amount  of 
water  which  may  be  needed  and  especially  the  probable  behavior 
with  respect  to  necessity  for  drainage. 

As  regards  climate  in  its  relation  to  irrigation,  it  may  be  said 
that  irrigation  is  most  beneficial  and  is  absolutely  necessary  where 
there  are  droughts  prevailing  through  a  whole  or  part  of  the  crop 
season,  which  is  usually  the  case  where  the  rainfall  throughout 
the  year  is  less  than  10  to  15  in.  in  depth.  A  small  amount  of 


ECONOMIC  FEATURES  OF  IRRIGATION  279 

rainfall  means  as  a  rule  a  large  amount  of  sunshine.  As  the  sun 
is  the  source  of  all  life  and  growth,  it  follows  that  with  an  artificial 
supply  of  moisture  in  these  regions  where  the  sun  shines  nearly 
every  day,  the  plant  growth  must  be  rapid,  even  though  during 
much  of  the  year  the  climate  is  notably  cold.  It  is  a  matter  of 
surprise  to  note  how  successful  irrigation  is,  for  example,  in  portions 
of  Canada  where,  taking  the  year  through,  there  is  a  very  cold 
climate.  The  summer  season  though  short  is  notable  for  its  long 
hot  days.  Where  water  can  be  applied,  the  plant  development 
during  this  short  summer  is  extremely  vigorous,  thus  it  results 
that  irrigation  is  being  extended  into  the  Canadian  northwest; 
to  a  country  which  is  popularly  supposed  to  have  an  almost  artic 
climate  but  which  actually  produces  notably  large  crops  during 
the  short,  intense,  summer  period. 

The  largest  success  under  irrigation  is  attained,  of  course,  in 
the  truly  desert  areas  of  the  southwest,  where  the  climate  is  such 
that  plant  growth  continues  throughout  the  winter  season  with 
a  very  short  period,  if  any,  of  rest.  Here  crop  follows  crop  in  rapid 
succession;  alfalfa,  for  example,  can  be  cut  at  intervals  of  five  or 
six  weeks,  and  field  crops  may  be  had  in  rapid  rotation,  sometimes 
three  cultivations  on  the  same  ground  being  successful  during  each 
calendar  year. 

With  respect  to  the  crops  which  may  be  raised,  this  is  a  matter 
which  must  be  governed  not  only  by  the  character  of  the  soil  but 
very  largely  by  human  conditions,  namely,  those  of  transportation 
and  market.  In  attempting  to  develop  any  new  area,  it  is  to  be 
assumed  that  transportation  has  not  yet  been  fully  provided,  and 
the  question  to  be  given  serious  consideration  is  as  to  the  probability 
of  early  construction  or  improvement  of  railroads,  and  other  means 
of  taking  the  crops  directly  to  the  centers  of  population. 

In  some  localities  there  may  be  in  existence  a  local  demand  for 
crops  such  as  that  at  mining  camps  in  the  mountains.  In  others, 
there  may  be  need  of  forage  for  winter  feed  and  for  cattle  upon  the 
open  range.  For  most  localities  crops  should  be  selected  in  accord- 
ance with  the  means  of  getting  these  to  the  cities  and  towns  and  of 
selling  them  in  competition  with  similar  products  from  other  pro- 
ducing areas. 

It  is  a  common  mistake,  especially  in  pioneer  communities,  to 
attempt  the  raising  of  varieties  of  crops  which  have  been  successful 
elsewhere,  but  which  are  not  adapted  to  the  peculiar  conditions. 
The  farmers  coming  from  other  localities  naturally  try  to  utilize  the 


280      PRINCIPLES  OF  IRRIGATION  ENGINEERING 

results  of  former  experience,  and  do  not  realize  that  this  experience 
is  inapplicable  to  the  new  home. 

Many  farmers,  for  example,  have  been  successful  in  raising  grain 
by  the  ordinary  or  dry-farming  methods  and  do  not  appreciate  that 
the  cost  of-  irrigation  does  not  justify  continuing  in  this  line.  They 
do  not  keep  sufficiently  accurate  accounts  to  know  where  their  losses 
are  occurring,  and  may  keep  on  year  after  year  planting  those  crops 
which  are  not  netting  them  a  sufficient  amount  to  be  remunerative. 
It  is  this  failure  to  appreciate  the  relative  cost  and  values  of  various 
crops  which  has  led  to  the  lack  of  success  and  relatively  low  crop 
values  throughout  a  considerable  part  of  the  arid  regions. 

Permanence  of  Water  Supply. — All  values  rest  upon  the  water 
supply.  The  permanence  of  this  supply,  as  previously  noted,  must 
be  looked  into  not  merely  from  the  physical  side,  but  even  more 
carefully  from  the  legal,  in  order  to  have  proper  assurance  that  if 
water  is  found  to  be  in  existence  the  right  to  the  use  of  it  may  be 
perpetually  maintained.  The  permanence  from  the  physical  stand- 
point is  a  matter  which  may  be  inferred  only  from  an  examination  of 
records  of  the  past.  The  assumption  is  made  that  whatever  has 
occurred  in  the  past  will  probably  occur  again  in  the  future.  It  is 
necessary,  therefore,  to  obtain  every  possible  fact  concerning  the 
behavior  of  the  stream  from  which  water  is  to  be  obtained  and  of 
similar  streams  having  like  conditions.  If,  for  example,  it  has  been 
found  through  observations  carried  on  during  ten  years,  that  the 
average  flow  during  the  summer  is  1,000  cu.  ft.  per  second,  it  is 
assumed  that  this  average  will  be  maintained  for  another  ten  years. 

If  there  has  been  a  large  flood  upon  this  or  upon  a  similar  stream, 
provision  must  be  made  for  passing  such  flood  and  even  a  larger  one 
around  the  works.  On  the  other  hand,  if  a  drought  has  occurred 
allowance  must  be  made  for  a  similar  drought  with  the  possibilities 
that  it  may  be  somewhat  more  severe. 

Provision  must  be  made  for  all  of  these  conditions  based  upon 
the  fundamental  conception  that  nature  repeats  itself.  Our 
knowledge  is,  of  course,  confined  wholly  to  what  has  happened  in 
the  past;  we  make  all  plans  and  investments  upon  the  assumption 
of  the  permanency  of  natural  phenomena.  It  may  be  that  the 
period  during  which  observations  have  been  made  is  abnormal,  that 
is  to  say,  that  for  the  ten  years  of  observation,  there  may  be  more 
or  less  available  water  than  has  occurred  in  previous  decades  of  which 
we  have  no  exact  records.  This  is  the  chance  which  must  be  taken, 
but  experience  has  shown  that  by  allowing  a  reasonable  margin 


ECONOMIC  FEATURES  OF  IRRIGATION  281 

for  safety,  works  may  be  planned  and  built  upon  these  as- 
sumptions. 

Cost  of  Constructing  Works. — The  cost  of  constructing  works  is 
the  next  topic  in  order  after  considering  the  questions  of  feasibility  as 
regards  water  supply,  soil,  climate,  and  crops.  It  has  come  to  be  an 
axiom  that  this  cost  is  generally  greater  than  the  original  estimate. 
This  is  due  not  so  much  to  lack  of  care  and  thoroughness  in  prepar- 
ing estimates  as  to  the  fact  that  the  work  is  pioneer  in  its  character, 
and  improvements  are  suggested  or  new  needs  arise  so  rapidly  that 
works  which  were  planned  in  one  year  as  adequate  for  the  purpose 
in  mind  are  found  to  be  unsuited  or  undesirable  by  the  time  construc- 
tion is  well  advanced.  Many  changes  must  be  made,  or  additional 
details  provided  which  were  not  known  or  not  considered  necessary 
in  the  original  scheme.  It  is,  of  course,  possible  that  an  engineer 
may  plan  works  and  build  them  exactly  as  planned  and  within  the 
original  estimates,  but  this  condition  is  one  which  with  existing  irri- 
gation systems  does  not  take  place  under  ordinary  circumstances. 

The  engineer  may  plan  for  certain  works  to  meet  the  then  pre- 
vailing conceptions,  but  the  owners  or  financiers  usually  conclude 
that  it  is  necessary  to  add  certain  extensions  or  modify  details  such, 
for  example,  as  increasing  the  size  of  the  reservoir,  or  of  the  main 
canal,  or  adding  a  pumping  plant.  Thus,  as  a  result  the  works 
cost  more  than  anticipated,  and,  comparing  the  original  statements 
of  cost  with  the  actual  expenditures  made  it  is  seen  that  the  latter 
are  far  in  excess  of  the  estimates,  but  the  reasons  for  this  are  rarely 
given. 

Men's  ideas  with  reference  to  limits  of  practicability  or  cost  of  the 
works  have  rapidly  expanded.  The  small  canals  built  before  1900 
were  cheaply  executed,  the  structures  were  of  wood  and  of  tempo- 
rary character.  The  location  was  made  with  reference  to  keeping 
the  construction  cost  to  the  minimum  and  much  of  the  work  was 
done  by  the  farmers  themselves,  no  account  being  taken  of  what  is 
generally  termed  the  overhead  cost  including  that  of  planning  and 
organization  of  the  work. 

At  the  same  time,  the  estimates  of  the  area  watered  were  very 
liberally  made.  If  some  water  was  provided  for  a  farm,  it  was 
habitually  stated  that  the  entire  area  say  of  160  acres  was  under 
irrigation,  even  though  water  had  only  been  as  a  matter  of  fact 
applied  to  a  portion  of  it.  The  capacity  of  the  canal  might  not  be 
enough  to  supply  all  of  the  lands  which  were  claimed  to  be  irrigated. 
For  these  reasons  the  cost  per  acre  of  irrigation  was  stated  at  an 


282      PRINCIPLES  OF  IRRIGATION  ENGINEERING 

extremely  low  price,  less  than  $15  per  acre.  Beginning  about  the 
year  1900,  a  cost  of  $20  per  acre  for  irrigation  was  considered  high, 
but  when  it  began  to  be  appreciated  that  the  land  with  a  sure  water 
supply  would  yield  a  large  return  on  a  value  of  $50  or  even  $100 
per  acre,  it  was  recognized  that  larger  investments  in  construction 
would  be  justified.  Year  by  year  the  limits  of  assumed  feasibility 
have  been  increased,  so  that  by  1905,  it  was  assumed  that  $30  per 
acre  was  large,  then  $40  per  acre,  and  finally  by  1910,  a  cost  of  rec- 
lamation of  $60  per  acre  was  not  considered  prohibitory,  for  lands 
especially  in  the  southern  part  of  the  country.  In  fact,  when  con- 
sideration is  had  of  the  great  value  of  orchard  lands  an  expenditure 
of  $100  or  more  per  acre  to  provide  water  is  feasible.  In  semi- 
tropical  lands,  for  example,  in  the  Hawaiian  Island,  where  pumping 
plants  have  been  erected  for  raising  water  for  irrigation  to  a  height 
of  550  ft.,  an  outlay  of  several  hundred  dollars  per  acre  is  not  con- 
sidered out  of  the  ordinary. 

In  the  northern  temperate  regions,  for  example,  in  Colorado  and 
Montana,  for  the  ordinary  field  crops  an  investment  of  $40  to  $60 
per  acre  may  be  now  considered  as  large  but  not  prohibitory.  This 
may  be  increased  notably  for  warmer  regions  with  longer  crop 
season,  such  as  those  of  southern  Idaho,  and  portions  of  Oregon  and 
Washington.  Going  south  from  here  to  points  as  in  Arizona  and  Cali- 
fornia, where  crops  grow  throughout  the  greater  part  of  the  year,  an 
increase  of  50  per  cent,  in  the  amount  above  named  may  be  con- 
sidered as  moderate. 

If  estimates  are  based  on  the  crop  production  of  thoroughly  ir- 
rigated lands  it  can  readily  be  seen  that  these  give  a  good  income  on 
an  investment  of  from  $200  to  $500  per  acre,  so  that  theoretically, 
the  figures  above  given  could  be  increased  several  fold,  but  as  a 
matter  of  fact,  under  existing  conditions,  it  is  hardly  safe  to  figure 
on  this  basis,  although  it  is  possible  to  look  forward  to  a  time  when 
far  larger  investments  than  now  considered  wise  will  be  the  rule  rather 
than  the  exception. 

Other  Costs. — It  must  not  be  assumed  that  the  cost  of  an  irriga- 
tion system  is  simply  that  of  the  engineering  or  construction.  There 
are  other  costs  which  may  equal  or  exceed  these  and  neglect  of 
which  in  the  preliminary  estimates  frequently  leads  to  financial 
ruin.  These  are  the  somewhat  vague  and  intangible  expenses 
of  the  organization,  the  so-called  overhead  charges,  especially  of 
commission  and  interest  upon  bonds,  or  upon  other  securities 
issued  for  construction  purposes.  It  is  not  infrequently  the  case 


ECONOMIC  FEATURES  OF  IRRIGATION  283 

that  after  the  engineer  has  carefully  estimated  all  of  the  construction 
cost  and  has  allowed  15  per  cent,  or  20  per  cent,  for  contingencies, 
the  business  man  must  double  this  to  cover  the  items  above  noted. 

Taking  the  ordinary  conditions  of  private  irrigation  systems 
it  may  be  said  that  assuming  the  engineer's  estimate  of  construction 
at  100  per  cent.,  the  other  items  to  be  added  will  be  about  as  follows: 

Preliminary  examinations,  organization  and  promotion,  10  per 
cent. 

General  administrative,  10  per  cent.  This  is  after  the  funds 
have  been  raised,  the  general  plans  determined  upon  and  construction 
carried  to  completion. 

Interest  on  bond  issue,  20  to  30  per  cent.  This  is  assumed  to 
cover  most  of  the  construction  cost,  and  is  estimated  at  6  per  cent, 
per  annum  on  the  period  required  in  the  construction  of  large 
systems. 

We  thus  have  from  40  to  50  per  cent,  of  the  construction  cost 
to  be  added  at  the  time  when  the  works  are  completed. 

Beginning  with  the  time  of  completion  of  the  works  and  the 
beginning  of  active  irrigation  from  then  on  is  the  period  of  greatest 
difficulty  and  stress.  Settlement  of  the  lands  is  usually  slow,  the 
farmers  must  experiment,  the  markets  are  to  be  established,  and 
five,  ten  or  more  years  may  elapse  before  the  land  is  completely 
irrigated  and  the  farmers  are  able  to  make  notable  payments. 
During  this  time  the  cost  of  operation  and  maintenance  has  been 
large  and  this  with  the  interest  on  bonds  or  other  securities  may 
amount  to  75  per  cent,  or  even  100  per  cent,  of  the  actual  construc- 
tion cost. 

Markets  and  Transportation  Facilities. — As  before  stated,  the 
question  of  markets  and  of  transportation  facilities  must  be  con- 
sidered in  any  irrigation  scheme.  These  are  not  usually  at  hand 
when  the  project  is  under  consideration,  but  come  as  a  natural  out- 
growth of  the  development  of  irrigation.  As  soon  as  it  is  apparent 
that  products  of  the  soil  are  to  be  handled  in  quantity,  there  is 
aroused  an  interest  in  the  matter  on  the  part  of  transportation 
agencies  and  markets  are  created  in  accordance  with  the  products 
available.  It  is  necessary,  therefore,  to  place  large  reliance  upon 
these  future  developments. 

Any  considerable  area  of  desert  land,  say  50,000  acres  more  or 
less  to  be  brought  under  cultivation,  will  attract  railroad  builders 
and  one  or  more  railroads  will  naturally  be  built  into  the  territory 
as  soon  as  the  success  of  the  works  is  assured.  There  is,  of  course, 


284      PRINCIPLES  OF  IRRIGATION  ENGINEERING 

an  element  of  uncertainty  in  this  matter,  but  it  is  sufficient  to  call 
attention  to  the  fact  that  it  is  not  possible  in  advance  of  construction 
to  be  sure  of  railroads  and  markets  and  a  certain  amount  of  chance 
may  properly  be  assumed,  and  in  fact  is  always  assumed,  in  the 
building  of  these  works  of  reclamation. 

The  success  of  the  farmer  and  his  consequent  ability  to  repay  the 
building  cost  of  the  works  and  the  expense  of  operation  and  main- 
tenance, are,  of  course,  dependent  upon  his  ability  to  dispose  of  the 
crops.  On  the  other  hand,  there  is  a  certain  amount  of  elasticity 
in  that  the  crops  can  be  varied  from  year  to  year  to  suit  the  changing 
conditions.  If,  for  example,  at  first  there  are  no  railroad  facilities, 
he  can  raise  forage  crops  which  are,  as  a  rule,  eagerly  sought  by  the 
stockmen,  and  if  prices  are  sufficiently  low,  cattle  and  sheep  will  be 
driven  into  the  region  for  winter  feeding  or  fattening.  As  trans- 
portation facilities  improve,  crops  can  be  produced  which  may  be 
shipped  and  higher  and  higher  grades  of  perishable  fruits  can  be 
produced. 

Security  of  Investment. — All  of  these  considerations  of  feasibility 
or  practicability  lead  up  to  the  point  vital  to  the  investor,  namely, 
as  to  whether  the  money  spent  in  the  construction  of  irrigation  works 
will  be  returned  within  reasonable  time,  with  reasonable  profit,  and 
reasonable  interest.  In  general,  it  may  be  said  that  investments  in 
irrigation  works  properly  planned  with  reference  to  adequate  water 
supply  and  climatic  and  other  conditions  should  be  safe  and  prof- 
itable. Assuming  that  care  and  intelligence  have  been  displayed  in 
guarding  the  rights  to  the  water,  in  planning  and  building  the  works, 
and  in  adapting  them  to  the  peculiar  conditions,  there  is  nothing 
which  should  be  on  a  similar  financial  basis,  because  of  the  large 
annual  profits  which  may  be  derived  by  the  farmers  from  intelli- 
gently tilling  the  soil. 

Under  the  above  assumptions,  the  security  and  the  value  of  the 
works  to  the  community  is  beyond  question,  as  they  are  vital  not 
merely  to  production  of  crops  but  to  the  maintenance  of  population 
and  even  to  the  sustenance  of  life  itself.  As  to  whether  they  will  be 
profitable  or  not,  this  is  another  matter.  It  has  already  been  stated 
that  the  speculative  profits  or  those  growing  out  of  the  increase  in 
Values  comes  to  the  owner  of  the  lands  rather  than  to  the  builders 
or  owners  of  the  water-supply  system  as  distinguished  from  the 
landowners.  The  fact  that  most  irrigation  projects  as  such  have 
not  been  financially  successful,  does  not  reflect  upon  the  value  of 
the  investment,  but  rather  upon  the  lack  of  experience,  skill  and 


ECONOMIC  FEATURES  OF  IRRIGATION  285 

good  judgment  in  planning  and  building  and  operating  the  works. 
To  illustrate  the  point  in  mind,  the  irrigation  works  may  be  com- 
pared to  the  foundations  of  a  building.  Upon  them  rests  the  whole 
social  and  economical  superstructure.  Their  value  and  importance 
is  beyond  doubt,  but  like  the  foundations  of  a  building  they  may 
return  very  little,  if  any,  direct  profits  on  the  investment.  These 
come  from  the  superstructure  itself,  which  is  carried  by  the  founda- 
tions. Of  course,  if  they  are  poorly  designed  and  imperfectly  exe- 
cuted, everything  built  upon  them  is  correspondingly  weakened. 

Summing  up  the  entire  consideration  of  economic  features,  it 
may  be  said  that  we  are  still  in  what  may  be  termed  the  pioneer 
stage  of  development,  particularly  in  the  solution  of  the  great 
problem  of  the  proper  relation  of  all  these  matters  one  to  the  other. 

In  each  one  of  the  separate  details  large  experience  has  been  had 
and  it  is  possible  to  find  a  man  skilled  in  engineering  or  in  economics 
who  can  successfully  handle  each  one  of  these  questions  or  even 
several  of  them,  but  when  it  comes  to  the  entire  combination,  few 
men,  if  any,  have  had  the  experience  in  all  the  parts  needed  to  pro- 
duce success.  In  other  words,  each  separate  part  may  be  properly 
designed  and  operated  but  the  whole  assemblage  may  be  a  failure. 

In  this  respect  the  situation  is  very  similar  to  that  in  the  organi- 
zation of  a  large  manufacturing  establishment  which  has  been 
initiated  by  men  who  have  not  been  brought  up  in  this  particular 
line  of  business.  It  may  be  assumed  that  each  one  of  a  group  of 
several  experts  is  competent  in  his  specialty;  for  example,  one  man 
in  designing  and  installing  the  machinery,  another  man  in  the 
purchasing  of  raw  material,  another  in  selling,  etc.,  but  these  men 
have  never  before  been  associated  together  and  have  not  grown 
up  with  this  particular  combination.  Thus,  we  have  the  condition 
where  each  part  may  be  excellent  in  itself  but  the  lack  of  coopera- 
tion or  of  so-called  " team-play"  prevents  the  success  of  the  whole, 
although  this  lack  of  success  is  not  attributable  to  the  defect  in  any 
one  operation.  It  is  this  condition  which  prevails  on  many  of  the 
large  irrigation  projects  in  that  the  whole  assemblage  of  parts  and 
their  successful  operation  is  still  largely  in  the  experimental  stages. 

Ultimate  Results. — The  engineer  may  derive  satisfaction  from  his 
work  in  irrigation  not  only  from  the  financial  returns  but  from  the 
consideration  of  the  fact  that  these  works  have  the  largest  direct  bear- 
ing upon  the  material  prosperity  not  only  of  individuals  and  commu- 
nities, but  of  the  state  and  nation.  They  form  the  foundations 
upon  which  are  built  agricultural  communities,  villages,  lines  of 


286      PRINCIPLES  OF  IRRIGATION  ENGINEERING 

railroad,  and  the  whole  social  fabric,  embracing  not  only  the 
farmers,  but  all  of  the  trades  and  occupations  which  have  to  do 
with  transporting  or  manufacturing  the  materials  produced  by  the 
farmer,  or  designed  for  his  needs. 

The  engineering  works  thus  not  only  directly  make  opportunities 
for  homes  for  the  men  who  till  the  soil,  but  for  every  home  thus 
created  there  is  possibility  of  another  home  for  the  mechanic  or 
artisan  or  railroad  man  who  is  engaged  in  supplying  the  needs  of 
the  farmer  or  in  transporting  the  raw  and  manufactured  products 
from  or  to  the  farm.  To  the  investor  also  there  is  offered  oppor- 
tunity for  not  merely  increasing  his  capital,  if  intelligently  used, 
but  of  obtaining  this  increase  through  assisting  other  men  to  utilize 
the  natural  resources  which  otherwise  go  to  waste.  Finally,  to  the 
public  man  or  statesman,  there  is  no  subject  more  fascinating  or  more 
important  than  that  of  watching  and  aiding  in  the  development  of 
the  country  through  the  intelligent  conservation  and  use  of  these 
natural  resources. 


INDEX 


Acquiring  water  rights,  268 
Acre-foot,  definition,  27 
Advantages  derived  from  irrigation,  6 
Alignment  of  canals,  38 
Alkali,  effect  on  soil,  138 
Amount  of  water  required  for  irriga- 
tion, 34,  158 
Applying  water  to  the  land,  methods 

.of,  5 
Arid  regions  of  the  U.  S  ,  8 

topographic  features  of,  10 

soil  of,  10 

regions  of  the  world,  3 
Aridity,  causes  of,  8     . 
Arkansas  river  underflow,  119 
Arrowrock  dam,  Boise  River,  Idaho, 

250 
Automatic  gages,  160 

Banks,  care  of,  164 

erosion  of,  41 

material  for,  43 

roadways  on,  56 

slopes  and  widths  of,  41 
Belle  Fourche  project  dam,  225,  245 
Bench  flumes,  83 

Beneficial  use  of  water,  definition,  272 
Benefits  derived  from  irrigation,  4 
Berm,  definition  and  advantages,  41 
Bermuda  grass  for  protecting  banks, 

165 

Bigelow,  Prof.  Frank,  table  of  evapora- 
tion losses,  175 
Boring  and  test  pits  for  dam  sites,  192 

for  drainage  information,  147 
Bridges,  96 
Brush  and  log  dams,  204 

Canal  and  ditch,  definition,  5 
banks,  care  of,  164 

slopes  and  width,  41 
capacity,  35 

determining,  36 
channels,  sitting  of,  46 
cross-section  of,  38 
embankments,  39-43 
lining,  55 
driers,  167 
structures,  classification,  61 

protection  of,  100 
systems,  definition,  102 


Canals,  alignment  of,  38 

and  laterals,  102 

cleaning,  165 

economic  construction  of,  37 

excavation,  47 

grades  and  velocity  of,  44 

lateral  draining  of,  57 

lined,  55 

location,  36 

measuring  devices  for,  97-99 

moss  in,  165 

narrow  versus  wide,  39 

operating     and     controlling     de- 
vices, 65 

priming,  164 

protection  against  seepage,  52-55 

right-of-way  for,  59 
Capacities,  computation  of  for  reser- 
voir sites,  188 
Capacity  of  canals,  35 

determining,  36 

of  culverts,  81 

of  drains,  147 

of  laterals,  105 

of  outlets,  248 

of  spillways,  197,  259 

of  turnouts,  70 
Care  of  banks,  164 
Cement  tiling  drains,  144 
Centrifugal  pumps,  120 
Character  of  water  supply,  15 
Check  system  of  applying  water,  6 
Checks  and  drops,  71-78 
Cippoletti  weirs,  in 
Classification  of  canal  structures,  61 
Classifying  excavation,  49 
Cleaning  canals,  165 
Clear  Lake,  Ore.,  dam,  226 
Climate,  soil  and  creeps,  278 
Climatic,  conditions,  14 
Closed  drains,  144 
Cold  Springs,  Ore.,  dam,  225 
Compacting  earth  dams,  218 
Compressed-air  pumping  plant,  127 
Conconully   dam,   Okanogan   project, 

218,  251 
Concrete  dams,  238 

drops,  74 

core  walls  in  earth  dams,  220 

flumes,  86 
Constancy  necessary  in  water  supply,  18 


287 


288 


INDEX 


Construction  of  bridges,  96 

of  canals,  37 

of  checks  and  drops,  71-78 

of  culverts,  80-83 

of  dams,  194-197 

of  earth  dams,  214 

of  fishways,  257 

of  flumes,  83-89 

of  headgates,  62 

of  masonry  dams,  232 

of  outlet  works,  248-262 

of  rock- fill  dams,  227 

of  siphons,  92-95 

of  sluice  gates,  79 

of  spillways,  79,  196,  258,  259-261 

of  tunnels,  81-92 

of  turnouts,  67 

of  water  cushions,  75 
Continuous  flow  system  of  water  dis- 
tribution, 153 
Contour  maps,  105 

for  reservoir  sites,  187 
Controlling  apparatus,  65 
Core  walls  in  earth  dams,  219 
Cost  of  canal  riders,  167 

of  constructing  irrigation  works, 
281 

of  excavating,  49 

of  hydroelectric  pumping  plants, 

131 

of  irrigation  by  windmills,  123 

of  pumping,  132 

of  operation,  167 

of  reservoirs,  184 

of  storage,  183 

of  test  pits  and  borings  for  dam 

sites,  193 
Crib  and  pile  dams,  207 

dams,  205 

Crop  values  increased  by  irrigation,  6 
Crops,  soil  and  climate,  278 
Cross-section  of  canals,  38 

of  laterals,  108 

of  masonry  dam,  235 
Cross-sectional  area  of  culverts,  81 

area  of  streams,  determining,  31 
Croton   watershed,   New  York   City, 

dam,  245 

Crushing  strength  of  stone,  241 
Culverts,  80-83 
Curved  masonry  dams,  239 
Curves  in  canal  construction,  38 
Cut-off  trenches  for  earth  dams,  222 

walls,  67 
Cycles  of  precipitation,  20 


Dam  construction,  194-197 
Dam  foundations,  191 

selection  of  proper  type  of,  199 

site,  surveys  of,  190 


Dam  sites,  borings  and  test  pits,  192 
Dams,  crib,  205 
earth,  211-225 

construction  of,  214 

core  wall,  219 

cut-off  trenches,  222 

drainage,  224 

dikes,  224 

examples,  225 

foundation,  211 

limit  of  height,  225 

materials  for,  212 

placing  materials,  214 

protection  of  slopes,  223 

puddle  core,  221 

section  of,  213 

seepage  under,  213 

site  for,  211 

water-tight  face,  221 
elementary  forms  of,  200 
framed,  208 
internal  stresses,  240 
kinds  of,  200 
log  and  brush,  204 
masonry,  232-247 

concrete,  238 

curved,  239 

foundations,  235 

heights,  245 

multiple  arch,  239 

overflows,  242 

protection  of  toe  from  erosion, 
244 

rubble  concrete,  223 

safe  foundation  limits,  214. 

section,  235 

typical,  245 
principal    storage    and    diversion 

table  of,  247 
rock-fill,  226-231 

advantages  over  earth  dams,  227 

foundation,  228 

materials,  228 

section  and  slopes,  229 

seepage,  231 

site,  227 

water-tighting,  230 
timber,  200-210 

conditions  of  stability,  203 

limits  of  height  of,  209 

types  of,  204 

use  of,  202 

water-tightness,  204 

when  applicable,  202 
Delivery  boxes,  no 

points  of  water,  109 
Depth  of  drains,  148 
Desert  Land  Act,  provisions  of,  265 
Design  of  spillways,  259 
Determination  of  storage  required,  179 
of  storage  supply,  171 


INDEX 


289 


Dikes,  224 

Discharge  of  streams,  computing,  31 
Distance  between  drains,  149 
Distributaries,  flume  and  pipe,  113 
Distribution  of  water,  152 

continuous  flow  system,  153 

periodic  rotation  system,  154 

systems,  103 

Ditch  and  canal,  definition,  5 
Drainage,  benefits  of,  138 

classification,  136 

effects  of,  on  soil,  142 

investigation,  146 

lateral,  of  canals,  57 

need  for,  136 

of  earth  dams,  224 
Drains,  capacity  of,  147 

depth  of,  148 

distance  between,  148 

grades  and  velocity  of  flow,  150 

open  and  closed,  143 

relief  and  intercepting,  145 
Drops  and  checks,  71,  78 

notched,  77 

vertical  and  inclined,  71 
Droughts  and  floods,  32 
Duty  of  water,  definition,  157 

Early  methods  of  irrigation,  3 
Earth  dams,  211-225 

construction  of,  214 

core  wall,  219 

cut-off  trenches,  222 

drainage,  224 

dikes,  224 

examples  of,  225] 

foundation,  211 

limit  of  height,  225 

materials  for,  212 

placing  materials,  214 

protection  of  slopes,  223 

puddle  core,  221 

section  of,  213 

seepage  under,  213 

site  for,  211 

water-tight  face,  222 
East  Park  dam,  237 
Economic  questions  in  storage,  181 
Elementary  forms  of  dams,  200 
Embankments,  39,  43 

consolidating,  49 
Equivalents  in  hydraulic  computation, 

29 
Erosion  at  flume  ends,  88 

of  canal  banks,  31 

protection  of  dam  toe  from,  244 

of  spillways  against,  261 
Estimating  cost  of  excavating,  49 
Evaporation  losses,  106 

loss  in  storage,  175 
Evaporation's  effect  on  runoff,  23 
19 


Excavating,  estimating  cost  of,  49 

machinery,  48 
Excavation,  classifying,  49 

of  canals,  47 

specifications  for,  50 
Experience  valuable  in  irrigation,  7 

Facing  earth  dams,  221 

rock-fill  dams,  230 
Farming,  intensive,  13 
Feasibility  of  irrigation,  275 
Fishways,  256 
Flash  boards,  65 
Flood  water,  value  of  storing,  18 
Flooding  system  of  applying  water,  5 
Floods  and  droughts,  32 
Flow  in  drains,  velocity,  150 
Flume  distributaries,  113 
Flumes,  83,  88 

and  trestles,  58 

rating,  in 

velocity  and  flow  of  water  in,  88 
Foundation  of  earth  dams,  211 

rock-fill  dams,  228 
Foundations  of  masonry  dams,  235 

for  dams,  191 

safe  limits  for,  241 
Forest  reserves,  10 
Framed  dams,  208 

Freezing,  effect  of  on  canal  lining,  55 
Frequency  of  irrigation,  156 
Fresno  scrapers,  48 
Furrow  system  of  applying  water,  6 

Gaging  station,  31 
Gasolene  and  oil  plants,  1 24 
Gate  towers,  250. 
Gates,  valves,  256 

character  of,  255 

operation  of,  252 

outlet,  location  of,  250 

vibration  of,  253 
Gila  river,  discharge  of,  1 6, 17 
Grades  and  velocity  of  canals,  44 

of  drains,  150 

Granite  Reef,  Ariz.,  dam,  242 
Green  river,  discharge  of,  16,  17 
Ground  water,  definition,  140 

Headgates,  62 

Height,  limit  of,  of  timber  dams,  209 
maximum,  for  pumping  for  irriga- 
tion, 135 

Human  element  in  irrigation  work,  162 
Huntley  water  power  pumping  plant, 

Hydraulic  computations,  list  of  equiv- 
alents, 29 

rams,  125 

sluicing,  216 
Hydroelectrical  power,  127 


290 


INDEX 


Hydroelectric  power,  computing,  129 
Hydrographic  conditions  limiting  stor- 
age, 172 

Intensive  farming,  13 

Intercepting  drains,  145 

Internal  stresses  upon  masonry  dams, 
240 

Irrigation,  amount  of  water  required 

for,  34 

benefits  derived  from,  4 
by  windmills,  123 
definition,  i 
feasibility  of,  275 
frequency  of,  156 
head,  definition,  107 
history  and  development,  i 
increases  land  values,  277 
in  the  U.  S.,  first  development,  3 
season,  length  of,  155 
system,  maintenance,  163 
systems,  human  element  in,  162 
versus  non-irrigation,  6 

Kennedy,  R.  G,  on  silting  of  canals,  46 

Land  and  water  ownership,  273 
Land  values,  276 

Lands,   arid,   preparation   of   for  irri- 
gation, 12 

Laguna  Dam,  67,  195 
Lateral  drainage  of  canals,  57 

systems,  surveys  for,  104 
Laterals,  102 

accessibility  to,  114 

capacity  of,  105 

cross-section  of,  108 

location  of,  107 
Laws,  of  early  times  regulating  water 

supply,  2 

Length  of  irrigation  season,  155 
Lined  canals,  55 
Lining  for  tunnels,  91 
Locating  an  irrigation  project,  13 
Location  and  type  of  spillways,  260 

of  canals,  36 

of  laterals,  107 

of  outlets,  248 
Log  and  brush  dams,  204 
Loss  by  seepage,  1 73 

Machinery  for  excavating,  48 
Maintenance,  cost  of,  167 

of  irrigation  systems,  163-169 
Maps  for  dam  site,  191 

of  reservoir  sites,  186 
Markets  and  transportation  facilities, 

283 
Masonry  dams,  232-247 

rubble  concrete,  233 

foundations,  235 


Masonry,  section,  235 

concrete,  238 

curved,  239 

multiple  arch,  239 

internal  stress,  240 

safe  foundation  limits,  241 

overflows,  242 

protection  of  toe  from  erosion,  244 

heights,  245 

typical,  245 
Material  for  canal  banks,  43 

for  flume  construction,  86 
Materials  for  dams,  194 

for  earth  dams,  selection,  212 
placing,  214 

for  rock-fill  dams,  228 
Measurement  of  water,  methods,  30 
supply,  26 
used,  1 60 
Measuring  devices,  97,  in,  161 

miner's  inches,  28 

streams,  31-32 

water,  methods  of,  27 
Mechanical  meters,  99 
Metal  flumes,  86 
Meters,  99 
Methods,  4 

of  acquiring  water  rights,  269 
Miner's  inch  definition,  28 

of  application,  5 
Minidoka  project,  loss  by  seepage,  etc., 

160 
Mining  and  irrigation  interdependent, 

13 

Moss  destruction  in  canals,  165 
Multiple  arch  masonry  dams,  239 

Newlands  Reclamation  Act,  266 
North  Platte  project,  loss  by  seepage, 

etc.,  1 60 
North  Platte  River  dam,  246 

Oil  and  gasolene  plants,  124 
Okanogan  project  dam,  218 
Open  drainage  ditches,  150 
Operation,  cost  of,  167 

of  irrigation  works,  152-169 
Operating  and  controlling  device,  c>5 
Organic  vegetable  matttr  lacking  in 

arid  soil,  12 
Orifice,  submerged,  112 
Orland  project,  Calif.,  dam,  237 
Organization  for  operation  of  irriga- 
tion system,  166 
Outlet  gates,  location  of,  250 

operation  of,  252 

vibration  of,  253 

character  of,  255 
Outlets,  248-262 

capacity,  248 

location,  248 


INDEX 


291 


Outlets,  of  gates,  250 

gate  towers,  250 

operation  of  gates,  252 

erosion,  252 

vibration  of  gates,  253 

character  of  gates,  254 

fishways,  256 

spillways,  258-262 
Overflow  masonry  dams,  242 

spillways,  79 
Ownership  of    water  apart  from    the 

land,  273 
Owl  Creek,  S.  D.,  dam,  225 

Pathfinder,  Wyo. ,  dam,  246 
Permanence  of  water  supply,  280 
Permanent  canal  structures,  61 
Permeability  of  canal  banks,  43 
Periodic  droughts,  32 

rotation  system  of  water  distri- 
bution, 154 
Piling  core  walls,  220 
Pipe  distributaries,  113 
Points  of  delivery  of  water,  109 
Possibilities  derived  from  irrigation,  6 
Power  for  pumping,  121 
Precipitation,  cycles  of,  20 

at  Salt  Lake  City,  20 
Preparing  land  for  irrigation,  12 
Priming  canals,  164 
Priority  rights  protected,  271 
Protection  of  canal  structures,  100 

of  priority  claimants,  271 
Puddle  core  walls,  221 
Pumping,  cost  of,  132 

feasibility  of,  134 

for  irrigation,  maximum  lift,  135 

plants,  116-135 

plant  at  Huntley  Montana,  126 
at  Minidoka  Project,  Idaho,  130 

power  for,  121 

steam  power  for,  123 

systems,  water  supply  for,  117-119 
Pumps,  character  of,  120 

Quality  of  water  supply,  33 

Ramming  earth  dams,  219 

Rainfall  and  runoff,  ratio  between,  21 

divergence  in,  19 
Rate  of  flow,  definition,  27 
Rating  flumes,  in 

Ratio  between  rainfall  and  runoff,  21 
Recording  systems,  167 
Records  of  stream  flows,  198 
Relief  drains,  145 
Reservoir  losses,  174 

site,  choice  of,  188 

sites,  surveys,  186 

computation  of  capacities,  188 
Reservoirs,  requirements  for  sites,  185 


Reservoires,  shallow  versus  deep,  189 

table  of  costs  of,  184 
Ridges,  103 
Right-of-way,  115 

for  canals,  59 

Rights  to  water,  method  of  determina- 
tion, 264 

Riparian  rights,  267 
Rivers,  action  of  waters  of,  16 

underflow  of,  119 
Roadways  on  canal  banks,  56 
Rock-fill  dams,  226-231  * 

advantages  over  earth  dams,  227 

sites,  228 

foundation,  228 

materials,  228 

section  and  stapes,  229 

water-tighting,  230 

seepage,  231 

Roosevelt  dam,  Ariz.,  245 
Rubble  concrete  dams,  233 

masonry  dam,  typical,  234 
Runoff  affected  by  evaporation,  23 

amount  possible  to  be  stored,  172 

annual,  170 

comparison  of,  26 

definition,  20 

in  inches,  definition,  29 

influences  affecting,  21 

on  different  watersheds,  23 

ratio  of,  to  storage  capacity,  177 

Sagebrush  for  wind  shield,  12 
San  Leandro,  Calif.,  dam,  225 
Salt  Lake  City,  annual  precipitation 

at,  19,  20 
Valley,  first  irrigation  in  the  U.  S., 

Salt  River  project,  Ariz. ,  dam,  246 
Screen,  100 

Salts  in  water  supply,  33 
Second-foot,  definition,  28 
Section  of  earth  dam,  213 

of  rock- fill  dam,  229 
Sections  and  slopes  of  some  principal 

canals,  47 

Security  of  investment,  284 
Seepage,  guarding  against,  101 

loss  by,  5,36,  106,  159,  173 

prevention  of  under  earth  dams, 
213 

protection  against,  52-55 

through  earth  dam,  219 

through  rock-fill  dams,  231 
Shoshone  dam,  Wyoming,  197,  246 
Side-hill  flumes,  84 
Silt,  prevention,  66 
Silting  of  channels,  46 
Siphon  foundations,  94 

materials,  95 
Siphons  and  inverted  siphons,  92-95 


292 


INDEX 


Site  for  earth  dams,  211 

Sites  adapted  to  rock-fill  dams,  227 

for  dams,  190-199 

for  reservoirs,  185-188 
Sluice  gates,  66,  79 
Slopes  of  earth  dams,  protecting,  223 

of  rock-fill  dam,  229 

Soil,  effects  on,  of  alkali,  138 

of  drainage,  142 

of  the  arid  regions  of  U.  S.,  10 

studying  in  drainage,  150 
Source  of  water  supply,  15 
Specifications  for  excavation,  50 
Spillways,  79,  196,  258-262 

requirements,  258 

design,  259 

capacity,  259 

location  and  type,  260 

grades  and  velocity,  261 

erosion,  261 

Stability  of  timber  dams,  203 
State  control  of  water,  266 
Steam  power  for  pumping,  123 
Stone,  crushing  strength  of,  241 
Storage  capacity,  ratio  of  runoff  to,  177 

cost  of,  183 

economic  questions  in,  181 

hydrographic  conditions  limiting, 
172 

losses  from  seepage,  173 
from  evaporation,  175 

of  flood  water,  18 

required,  determination  of,  179 

supply,  determination  of,  170 
Strawberry  River  dam,  221 

Valley  tunnel,  89 
Steam  flows,  records  of,  198 

measurement,  32 

Streams,    determining    cross-sectional 
area,  velocity  and  discharge, 

31 

underflow  of,  118 
Sub-irrigation,  6 

Sudbury  River,  Boston,  dam,  245 
Surface  drainage,  136 
Surveys  for  distribution  systems,  104 

of  dam  site,  190 

of  reservoir  sites,  186 
Susquehanna  River,  discharge  of,  16, 17 
Systems  of  applying  water,  5,  6 

Tabeaud,  Calif.,  dam,  225 
Table,  cost  of  reservoirs,  184 

monthly  evaporation  losses,  176 
mean  annual  runoff  for  various 

water-sheds,  24,  25 
principal    storage    and   diversion 

dams,  247 
sections     and     slopes     of     some 

principal  canals,  47 
Temporary  canal  structures,  61 


Test  pits  and  borings  for  dam  sites,  192 
Timber  dams,  use  of,  202 

where  applicable,  202 

conditions  of  stability,  203 

water-tightness,  204 

types  of,  204 

limits  of  height  of,  209 
Topographic  features  of  arid  region  of 
U.  S.,  10 

surveys  for  lateral  systems,  104 
Towers,  gate,  250 
Transportation  facilities,  283 
Trestle  flumes,  84 

Truck ee-Carson  project,  loss  by  seep- 
age, etc.,  1 60 
Tunnels,  89-92 

lining  for,  91 

Turbines  efficiency  of,  131 
Turnouts,  67 
Typical  masonry  dams,  245 

Umatilla  project,  Ore.,  dam,  246,  249 

loss  by  seepage,  etc.,  159 
Uncompahgre  Valley  tunnel,  89 
Underground  drainage,  136 
Underflow  of  streams,  118 
Undulating  areas,  103 
Uniformly  sloping  planes,  103 
United  States,  arid  regions  of,  8 
early  irrigation  works  in,  3 
origin  of  water  rights  in,  264 
rainfall  of,  19 

Reclamation  Service  canals,  47 
Service,    specifications    for  ex- 
cavation, 50-52 

Units  of  water  measurement,  27 
Upper  Deerflat  Reservoir,  Idaho,  dam, 

245 
Upward  pressure  in  masonry  dams,  239 

Valves,  gate,  256 
Vegetable  growth  in  canals,  166 
Velocities  and  grades  in  canals,  44 
Velocity  and  flow  of  water  in  flumes, 

88 

of  streams,  measuring,  31 
Vibration  of  outlet  gates,  253 

Wasteways,  79 

Water,  "beneficial  use"  rule,  267 

common  property  of  all,  265 

cushions,  75 

delivery  schedule  at  Villiston,  N. 
D. ,  plant,  157 

distribution,  152 

continuous  flow  system,  153 

periodic  rotation  system,  154 

duty  of,  definition,  157 

loss  in  transit,  52,  53 

losses,  measurements  of,  159 

measurement,  methods,  30 


INDEX 


293 


Water  measurement,  units  of,  27 
methods  of  measuring,  27 
plane  portrayal,  147 
points  of  delivery,  109 
power  for  pumping,  125 
proper  amount  to  use,  158 
rights,  definition,  263 

origin  of  in  U.  S. ,  264 

riparian  rights,  266 

acquisition  of,  268 

theory  upon  which  granted,  271 

apart  from  lands,  273 
state  control  of,  266 
soluble  salts  in,  33 
supply,  amount  required,  34 

for  pumping  systems,  117-119 

permanence  of,  280 

priority   of   appropriation,    266 

measurement  of,  26 

quality  of,  33 

source  and  character  of,  15 

study  of,  18 


Water-tight  face  of  earth  dams,  221 
-lighting  rock-fill  dams,  230 
-tightness  of  timber  dams,  204 
under-ground  fallicies  concerning, 

118 

used,  measurement  of,  160 
velocity  and  flow  of  in  flumes,  88 
-shed,  character  of,  22 
-sheds,   varying  runoff  on,  23-25 
Weight  of  masonry  dams,  241 
Weirs,  rectangular  and  Cippoletti,  in 

use  of,  98 

Wells,  test,  for  drainage,  150 
Williston,   N.    D.,   schedule  of  water 

delivery,  157         / 
Windmills,  123 

Yadkin  river,  discharge  of,  16,  17 
Yakima  project,  loss  by  seepage,  etc. , 

1 60 
Yuma  siphon,  95 


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